It is a good idea to change the oiler plastic parts on the cam, if never done before.

the modulator has a rubber diaphragm that may break. It has to be changed I think the whole thing, cost about 60 euros over here from MB dealer.
Take of the plastic cap off where the vacuum tube goes and if it is oily, then it leaks and can produce irregular smoke from the exhaust.
It takes 5 min to replace it, just make sure the inner piston is at the same length as the old one as here you adjust the smoothness of the gear changes (if too smooth the gear may slip and that is no good).
I just had a case like this, although I have only experience in the 116, 123 and 107 chassis.

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MB 350 SL 2.8 -72
MB E220 -95
MB 230 E -82
MB 450 SEL -80 (project)