problem with STM Clutch slave? HELP!

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So to the boards advice in another thread I ordered an STM clutch slave and decided to put it on this rainy Friday (party central over here!).

The directions are pretty much worthless, though it does come with a nice picture of how to assemble the pre-assembled unit

I did NOT install the spacer that comes with it for pre-2000 bikes. The depth of the piston is very close to that of the factory unit.

Now, here is the issue: The factory slave butts against the motor around the pin coming out of the bike that goes to the clutch - the piston is internal. The factory unit even includes a nice o-ring to seal against the motor. The STM unit has nothing of the sorts - the piston appears to be external. When sliding the pin into the STM unit and mounting it to the bike there is a gap between the STM piston and the body of the bike. This gap is probbaly to let the piston in and out - doesn't that risk grime building up on the pin?

Do i have the right STM unit? did I install something wrong?

thanks for the help!

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here is a pic of the STM unit:

[StavesacredarK]

Wow That Shure Dosn't Make Since, And Ya Tha Angle Of Grime Sling From Your Chain Is Right There!!!

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FYI: on another board there was a meber thinks the yoyo unit seals like the factory unit.