The 112 and 113 motors use an automatic start function that also can cause some problems. If the instantanoeus current loading is too great it stops the starting activity. Mercedes solution is to lube the starter ring gear with a special non magnetic antiseize.

If the voltage stays during the cranking attempt you might want to check the above. There is a service bulletin on the issue and it has been discussed here so there should be archive info. I have only seen the instance once and it was accompanied by a swing from the tach above 2000rpms another condition noted in the bulletin.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician