Ken-

When I purchased the part from my mechanic, he told me that your symptom could also be a sign of a faulty monovalve. I would just swap out the insert and hope for the best, since the part is cheap and its easy to do.

I looked on fast lane and the "repair kit" for your car is the same as mine, same price too ($34).

Mike

__________________
'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E