>Could the recent patches to use udisks rather than pmount play a 
>role in this?

The problem turned out to be nominal dust and incomplete contact of 
the plastic pushbutton stem against the micro switch actuator head. 
After cleaning the inside of the mice, I spliced a carefully cut 
small piece of duct tape to the end of pushbutton stems. The 
pushbutton stems now make firm contact on the micro switch actuator 
head. The mice are acting like new. No missed clicks, no double 
clicks instead of single cicks, no dropped select-and-drag problems.

Darrell