the clutches in the 316 and 318's (especially early ones) were known to
warp or crack then judder when pulling away (think it was something to
do with the clutch material composition).
The condition is due to how the car's been driven, so say the previous
owner used to ride the clutch a lot, then it's quite concievable that
when you got it, the clutch was already well on it's way to wobbliness.
You say you had the clutch changed at 60k? To be honest, 100k miles
out of a clutch isn't bad going.
How many months are we talking about since you had it changed did teh
vibrations start again? If it was only within a few hundred miles you
should have taken it back to BMW?
The bottom line is it's the clutch again.
Only recently had the clutch changed in my wife's 316 Compact for this
same reason (her car was on about 73k miles when we had it changed).
I think the OEM clutch is made by SACHS, you might try getting it
replaced with another make.