...I'am Getting This Straight! You know there is Oil Getting onto the Clutch Disc, and You are Still Wondering Why the Clutch Slips?? Once a Clutch STARTS to Slip...There is NO 'Coming-Back' from it. Fix the Oil Leak and Install a All-New Clutch. To 'Save' the Flywheel...You may be able to 'Burn' the Oil out of the Steel 'Contact' Ring with a Torch, Or have it RE-Ground. I've been there before, but it was a ALL-Steel Flywheel.
...A Tip, this is also a Good Reason why one should NEVER 'PACK' a Ball PILOT Bearing with Grease!! The Grease gets Hot, Melts and the Centrifugal Force throws and runs it all over the Flywheel, Disc and Pressure Plate. BOOM! The Clutch Slips Right-Now...Forever! This Only takes a Little-Bit of LUBRICANT!!
Listen and understand Now, or do the Job Twice!
I Always run the McCloud 3-Finger P. Plate, Street/Competition Disc, and the 'Flat' Faced Throw-Out Bearing...and The 'MJ' Oilite Bronze Pilot Bearing.
MJ
P.S. ...The McCloud 3-Fingers of the Pressure Plate DO Have the Counter-Weights! I have Never had a Problem with Interference to the Bellhousing, and there has been NO Difficulty with the Clutch Release and Shifting gears at High RPM, where the Weights Add to the 'Holding/Grip' Pressure. But, NO Amount of Pressure will Overcome the LOSE of Friction.
Good-Luck with It!