axles popping: look at the CV joint boots on each axle (one at transaxle, one at wheel)
usually, the boot wears out or gets ripped, all the grease gets flung out of the CV joint, then you get popping when making turns.

clutch slipping: check the clutch cable adjustment; there should be about 1/8" of free play when the clutch is fully engaged. If there's no free play loosen the adjustment bolt until there is about 1/8" of free play. (otherwise, it's like driving around with your foot partially on the clutch pedal all the time)

It could be time to replace the clutch (clutch, pressure plate, resurface the flywheel, pilot bearing, throwout bearing).

I think the main transmission bearings that MattCook is refering to are the differential main bearings. (they're located where the axles go into the transmission) The only way to get oil from the transmission on to the clutch is through the input shaft seal; but, that is very unlikely because the oil in the transmission is not under pressure and the transmission oil level is always below that shaft seal.