As it clears right up with restart, I would check the OVP relay first.

When conditon develops, tap the relay a few and see what happens.
Archieves - "OVP relay.." There was a part change/upgrade on that item.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1D00YU6RY1JV0NGYI0&year=1995&make=MB&model=C-280-001&category=P&part=Overload+Relay

..and change the coil connectors mentioned = even if it is the relay.
As you just bought the car , the 3 common problems on that chassis are coil to plug connectors, OVP, and wire harness..
First two are low $$$.
Any/all can cause your complaint.