Lately, about 1/3 to 1/2 the time i start my 1985 1.9L, I hear and feel a
loud THUNK! from the rear.  It runs OK after the thunk.  I thought it was
most likely motor mount(s), but yesterday i was looking under the van and
saw a wet spot from coolant dripping from somewhere on the driver's side of
the engine.  Last night I came up with the unpleasant theory that the  two
could be related; the coolant could be leaking into the cylinder as well as
outside, and the thunk could be momentary hydro-lock.  Is this a
possibility?  It's a VW rebuilt engine wit 54,000 miles on it.