Brake clean is fine for that, i have used diesel fuel in a spray bottle in a pinch, just rinse it all out, tip it left and right and make sure its all drained out, run it with some fresh oil for a while then do another change to clear out anything that loosened up but didn't come out with the cleaning.
For installing the oil rotor what i use is a chain vise grip around the centrifugal clutch, but a strap wrench works, or even a ratchet strap around it to give some grip, those bolts don't get torqued that tight, i think its something like 7-9 ft lbs. So its not like super caveman tight on those they will snap off pretty easy if your not careful cause they are only m6 bolts.
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1984 Honda ATC200ES "Big Red"
1982 ATC200E "Hondie"
1988 TRX300FW "Project Quad" Still in progress....