See also:
Installing a new slave cylinder seal
Revised Slave Cylinder (Mar2005 Finally got some info)

By AndyW June2004:  Two FAQs in one as one probably has a bearing on the other.....discolouration / darkening of the clutch fluid and leaky slave cylinders (aka clutch release cylinder).

There has been lots of discussion on these subjects and whilst there are no definitive answers the most likely cause for both lie in the same place - the seal that prevents (should!) oil loss / dirt ingress past the clutch slave cylinder piston.

Discoloured Clutch Fluid:  Most likely cause is contamination with microscopic particles from the above mentioned seal...either as a matter of normal wear and tear or more likely due to abnormal wear due to dirt ingress past the seal (which is highly likely considering the exposure to crud that flies off the primary sprocket/chain). This 'theory' is supported by the fact that the discolouration settling out over time if the bike is not used (see photos below courtesy of Bayouboy).
At one point the source of these particles was suspected to be the rubber clutch hose but it became apparent that bikes fitted with braided hoses still suffered...back to that slave cylinder seal.

The Service Manual states that the clutch fluid should be changed every two years!.....my clutch fluid has been replaced three times to date with a full system flush each time...that's within 10 months of the bike being new and less than 5000 miles!!.  Now this may be coincidence or the result of previous system flushes but having used DOT5 (DOT4 is standard) I have now (May2004) covered 1000 miles with the clutch fluid remaining almost clean.....draw your own conclusions.
Update July 2004: Still on the same clutch fluid, around 2500 miles total now!.....it has darkened a bit and there are signs of particles again but it's lasted much better than ever before.  Probably totally unnecessary but I'll change the fluid again soon...sticking with the DOT5. (See further update at the bottom of the page)

Leaking Slave Cylinder:  A natural progression of wear and tear to the seal however a fair number of forum members have already experienced leaks of varying degrees at low mileages.  The first indications are drips of what appears to be oil (due to the mix with chain lube fling) from the bottom of the primary sprocket cover....in extreme cases riders have found themselves stranded with no clutch fluid, so check regularly!  I'm not absolutely sure of this but I believe that replacements for the seal in question have been modified from the original specification.

And a couple of photos I took just a couple of weeks after a fluid change

Always a good idea to check out the Service Manual...here's an extract............

(NB: 'Piston cup'...that'll be the seal!   And we all know what clutch/brake fluid does to paintwork!)

See Chapter 6 (page 87 onwards for instruction on clutch fluid replacement and
disassembly / rebuild of the clutch slave cylinder (clutch release cylinder)

A closer look at the offending article (sorry about the quality, from the Suzuki manual)

I think good advice would be to clean out the oily muck and grit that accumulates in the primary sprocket cover around the slave cylinder and clutch actuator rod on a regular basis......here's what I did (based on my posting on the forum Dec2003......bugger, bet it needs doing again!): Depending on what chain lube you use (and chain lube fling!) it's worth doing this clean-up job quite regularly (I do mine before every service now)

I removed the slave cylinder (I won't repeat instruction on this here as Brian has covered it already in his How to Avoid a Shattered Sprocket Cover article.....and don't forget the Service Manual!)... and immediately there were signs of what was to come.

A seal in the hole in the sprocket cover that the actuator rod comes
through and a slightly modified slave cylinder casing to take an 'O' ring in
the face that mates against the sprocket cover would have been a good idea.
(So would realising the camera was not set to auto focus - hence crap image!)

Followed by removal of the primary sprocket cover - the first thing to note is that I'd lost one of the three sprocket cover retaining bolts!, so as I've said lots of times...use thread lock on all bolts when reassembling. (that bolt cost me £1 !).....what a mess.

No evidence of any brake fluid leak which was a relief but I could see why the subject of 'dirt' ingression past seals had been discussed now. Once all the greasy sludge and debris had been cleaned away there was nothing to be seen that might suggest any problems.
The clean up is a messy job - I gently 'scraped' away as much of the sludge as possible with a screwdriver then worked paraffin (kerosene) into what was left with an old toothbrush...I was pretty liberal with the paraffin as there are no worries about it harming anything.  Then a final cleanup with a piece of rag.

Similarly with the slave cylinder I hooked out as much crud as I could from between the piston and the wall of the cylinder (a bit of wire like a straightened paper clip is ideal) being real careful not to damage the seal.  Then the toothbrush and paraffin treatment, using lots of paraffin to make sure all debris was flushed out from down the side of the piston.

And the compulsory 'after shot'.  The red arrow indicates the gap between the piston and cylinder wall and you can now see the seal further down.  I filled the gap with clean grease in the hope that no grit or anything abrasive will now get to the seal. I used Silkolene Pro RG2 Synthetic Racing Grease that is "..extra high temperature melting-point, lithium complex synthetic..." and waterproof etc.  Be careful in your choice of grease, read the tin, some oil based and other products are not recommended for use on seals.

Finally before reassembly......the manual says grease the actuator rod: I greased the full length of the rod, not to excess but fairly liberally.  I also lightly greased the area shown in the photo below to stop further corrosion (dry weather bike, mostly, with just 5000 miles on the clock at the time!) and the lug on the left.  It's important to make sure that the surfaces the spacer indicated by an arrow in the manual diagram above are clean...any grit could stop the slave cylinder seating properly.

Update 03 July 2004: Seven months on and the 7500 mile service booked for a couple of days time, I decided to give the slave cylinder a check over again.

All the grease I'd laid around liberally last time seems to have done the trick in keeping dirt out and no signs of fluid leaking round the piston seal.  I did note that there are signs of the seal wearing though indicated by a ring of dirty grease left at the seals furthest point of travel (indicated by the arrow in the photo below)....so regular checks still recommended.

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