Yeah thats right. Its actually very simple, only 4 parts:

1) There is the pivot arm (with included bolt) that screws into the timing chain cover. The bearing on this can fail, either partially by being rough to turn, or totally with it falling apart. This probably isnt a problem in your case, but check the bearing anyway.

2) The spring to provide the tension, not really a problem.

3) There is a shock absorber to stop the belt slapping around at idle when the power pulses are irregular. This fails a lot, the original versions had bushings which failed, and they also stop damping properly. 2 simple bolts to remove and replace, can probably do it without removing anything else on the om602.

4) The pulley, doesnt really fail, but the bearing went noisy on mine cuasin a high RPM whine so I replaced it.

Check the shock by holding it with your finger or a screwdriver. Replace it if your unsure, its cheap and probably getting worn out.

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1991 W124 250D - 130k Miles