Oil leak from clutch slave cylinder

After getting my GRiSO back together after fixing the oil leak in the rear main seal, that leak does seem to be fixed, but now I have a new one!

It’s coming from where the clutch slave cylinder bolts to the rear of the gearbox. Any ideas on how to fix it? Where is the seal for this? The cover itself doesn’t have a gasket; I assume it is sealed internally. Is there an O-ring or something inside? The parts diagram doesn’t show anything like that. The clutch is working perfectly now but oil the leak is driving me crazy! (Also it’s not hydraulic fluid that’s leaking, it seems to be gearbox oil.)

Bellagio has part # GU90706170 (???)
'O' ring 17.13 x 2.62

I don’t see where an O-ring would go? I can’t see it in the diagram in the parts catalog.

Sorry, my bad for assuming same parts for hydraulic clutch.

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Pg75 #14 - 976696 (Aprilia part #) - Engine bearing set.

This part is similar to Bellagio (Guzzi) part# GU04086100

Clutch Command Cylinder (slave) and Clutch Control Cylinder (inner part adjacent to thrust washer) are different between our bikes.

On all of the six speeds the slave is sealed by an o-ring that goes around the outer cylinder and is squished into a machined countersink around the orifice in the end case the slave slides in to.

As you say if it is listed in the parts list it's bloody hard to find! While I can't remember the exact size it's something like the OD of the spigot of the slave and has a X-section of something like 2.5mm. Really though it's *Exact* size isn't important. It's the fact that it isn't so skinny it doesn't seal in the countersink and also isn't so fat it doesn't allow the slave to bolt down flush to the case.

Take the slave off, (Probably best and easiest to just pull the swingarm again.) and measure the slave spigot. Then nip down to the bearing factor and buy three or four o-rings that are close dimensionally with slightly differing X-sections both metric and close imperial and find the one that feels best when you slide the slave into place, (You want it to slip in but hold the flange of the slave a few thou proud of the case to allow for crush.) then use that one and smear a tiny film of Threebond on the mating surface of the slave, bolt it up and be done with it. It doesn't, (Or shouldnt!) need to take any 'Pressure', it just needs to mate so it can seal.

Pete

Thanks so much Pete! That’s exactly what I needed to know! I couldn’t find that info or pic of the O-ring anywhere. I must have lost it when I took it apart.

O-ring has been fitted. Will get some miles on it on the weekend to confirm the leak is finally fixed!