Unless the leak is pretty severe, it's not very likely that the clutch will be affected. The oil will run down the rear surface of the oil pan and/or the front of the flywheel, but unless enough oil slings off to saturate the area inside the bellhousing, it will be difficult for it to find its way onto the area where the clutch meets the flywheel.
My 59 model 3800 flatbed came to me after a "rebuild" by the PO, who left one flywheel bolt out. Those bolt holes bypass the rear main seal, so there was a massive leak. The clutch began to slip within a couple of weeks, but the engine was leaking about a quart of oil to every tank of gas, and it was leaving big puddles everywhere I parked it. Unless you've got that kind of leak, I doubt if your clutch will be in danger.
Jerry
