I want to replace the oem seal on the leaking clutch cylinder on my 996 with an X-ring style. I did this years ago on a 900SS and it worked a treat but I can't remember what size was required. Anyone know?
I think it fits all. I ordered one from Pro Twins at great expense (£8 inc postage) and their description is '916 quad ring clutch seal' so I reckon it will fit your ST4. The size seems to be 1" outer diameter, 3/4" inner, and 1/8" width. Armed with those dimensions you can probably source one elsewhere for 50p.