Ok, OK, I can't stand it! Time for an experiment. 

At lunch I went out to the parking lot. I drove the syncro westie
in turns right and left, steering wheel against the stops. Surface
was asphalt,damp from morning rain, somewhat irregular and rough. 
Speeds-nothing fast, just prudent parking lot walking equivalent. 
Tires: I have the oversize, chunky AT LT27x8.5x14s.

Diff lock off: No shuddering or binding. Steering effort is high 
toward the stops, which I always thought was due to the expanded 
footprint of the oversize tires. Other than that, nice smooth circles.

Diff lock on: Shudders, enough that I did not want to keep on doing 
this to the vehicle. Shuddering definately decreases as I approach 
straight line. No visible tire scuffs  on the asphalt, but it is
not a dry surface.

Incidently, from experience in recent snow and ice, I fully believe the 
drivetrain is fully operational...

Comments?

Tom F.
90 syncro westie
87 syncro gl
90 audi 200 tqw ia stage I