I just used a combination of these two kits, which one in particular just a matter of what will (or won't) fit... the "coarseness" dictated only by what stage it's at. A 1/2 round file helps too - but mostly as a sanding block for "buffing" out some of the lateral scoring left by the Dremel's habit of only spinning one way.
Dremel 686-01 Sanding Grinding Kit
Dremel 684-01 20-Piece Clean & Polish Kit
The clutch is one of those things that if it works - best to just leave it be... but Jim's (Manic Mechanic) sweet animation sure is handy: http://motorbicycling.com/f30/animat...haft-8939.html
lastly - tho you'll prolly be able to salvage most of the gaskets if you've never run the motor before you disassemble it, odds are you'll mess up the base gasket at least. In any case gaskets are inexpensive and the stock ones aren't that great anyway - with that in mind I'd pick up spares and make whatever ones you feel comfortable doing, with a quality material found at yer local auto parts store
Ya don't hafta
do alla this BTW (many don't bother) - tho it does help, I just think it fun as well as giving that hard-sought extra "oomph" outa these lil motors