bare in mind, i never (in 25,000 miles) checked the transmission oil level (oops!)

its probably the prop causing the wobbling - i'm not aware of any balence weights though.. i'd compare it to another 340 thoguh - they're definately not as smooth as 360s..

thunking doesnt ring a bell, but i used to get a bang if i pulled up the clutch harshly in 2nd gear (with no throttle). solution? dont pull the clutch up harshly in 2nd gear.

still think changing the clutch will do nothing, but its up to you to find out