Take the inspection plate off the tranny, look for oil spun onto your fly wheel. If there is none. Then It's not your rear main..........And not unless you got a really really bad rear main seal leak, your clutch won't start slipping. That's if you have a stock flywheel anyway. Stock fly wheels are normally solid. So if anything, It'll only spin oil in the tranny housing. You clutch is on the other side of a solid flywheel. So your safe unless oil starts dripping from the top of you tranny housing onto you clutch.