Jeff,

I suspect 2 or more of the screws holding the back of the speedometer
housing were loose before or when you reset your trip odometer the last
time. Most likely the fact that the speedometer is not tight with the
cluster housing resulted in the reset button for your trip odometer to be
pushed in too far.  If the speedometer was being held in tightly against
the cluster housing, you should not have been able to push the reset
button in far enough for it to get stuck behind the clear plastic
faceplate.

You might try holding on to the back of the speedometer while you push the
reset button from the front and see if you can reset the trip odometer.

Hope that helps.

The circuitry at the back of the speedometer is for the dynamic oil
pressure circuit board, which is inside the speedometer casing.

Michael
My VW web page:
http://www.velocity.net/~vickrail/moshevw.htm