I'm with guide rod mounts. Another way to tell is after a stop, when you first let off the brake, you can feel a little give as the mount moves.

I replaced mine last year. About a two hour job the first time, not too bad. Do a search.

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1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer