I wanted to point out that I have seen the intermediate shaft
slow down or stop from timing belt slip on two of my own 1.6 D
and TD's, so Mark, Bob Dennis and others are likely right on.

In one case the slip was announced through a screech and I
stopped immediately. Problem in this case was high friction in
oil pump, not belt tension. Changed oil pump and problem fixed.

In the second case problem was much more devious. I had
flickering oil light during highway driving. (This was on a
Quantum/Passat with the dual oil pressure sensors)
Culprit was occasionally slipping timing belt. After cleaning
out dirt and oil from inside the cover (Took a few cleanings)
the problem went away.

Cheers,
Martin