I drilled the (4mm dia) weep hole as a preventative measure, soon after taking delivery of my '05. All was good when I removed the slave cylinder. One observation - the slave body is approximately 1.3 mm smaller in diameter than the machined bore in the rear of the gearbox housing, so an alternative to drilling the weep hole may be to take a small file and make a groove in the bottom of the mating surface where the slave bolts to the gearbox. Then if the slave leaks, the fluid will travel back along to the joint and weep out there. Just a thought as there is not much room for error when drilling the hole.
I did my 99 with 53k on the clock. I caught my slave leaking before it had a chance to contaminate my clutch. Put in a used slave off of ebay--thought a weep hole would be good insurance. At 73k she still has not leaked.
I did the weep hole near 45K as a preventive procedure. I did it quite a few years ago when slaves were failing all over the place and taking out clutches. During the procedure I found that the slave was already leaking and the felt pad was already saturated. Since I was at a 'weep hole drilling party' with quite a few other guys, I reinstalled the defective slave, after cleaning it up (of course), and rode 300 miles back home. I ordered the slave and replaced it after 1K of additional riding with the new and improved slave..
I could see where the weep hole worked during the replacement. So, I can verify that the procedure will actually work. I have 95K on the bike know and I do inspect the area during service but I have not seen any trace of a new failure.
Had dealer drill mine at 16000km after I burnt out original clutch (well, I thought it was a sports armchair)... currently at over 80,000km's with no signs of an issue on the 2nd clutch plate (fingers crossed, touch wood.. etc etc)
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