Thud in the parking lot

["Carmen S. DeVito" <devitocs@epix.net>]

Any help appreciated on this.  
I have an 1988 5KCST w/70000mi.  In slow speed (Parking Lot) turns,
moving the wheel counter clockwise (left turn), I hear and feel a thud
and slight shift of the front end.  This will sometimes also happen on
straightening from a left turn.  I don't notice it at higher speeds.  No
clicking sound, so I don't think it's CV's.

I've checked the ball joints, bearings and bushings, nothing obviously
loose.
Shocks are less than one year old Bilsteins
Replaced the steering rack 2/96 (Blaufergnugen)
Replaced Lower Control Arm bushings & front bearings on 11/94 (57Kmi)
Could be early failure of the above but I can't tell.  Sound familiar to
anyone?

Also unrelated, I think, is a vibration in the front end only under
acceleration.  I can feel this through the wheel and the pedal.  One
mechanical thought it was a bad drive shaft, another said tranmission
mount.  I replaced the mount...

I really love the car but after replacing the tranmission this Summer,
my wife threatened to drive it in the river. :^)  

Thanks for the help and good reading.
Carmen
1988 5KCSt
1991 Porsche 911 C4 (AWD)