[JhwShark]

Great news!

A connection issue causing an Open circuit.

fyi...From the schematic (Start section): the wires on the starter go to two terminals.
1st is the big one that has a big red wire from the charging system, an almost as big black wire to the battery circuit, and a small red wire to the diagnostic connector.
2nd is a single wire that should be thin black with a yellow stripe that goes to a connection for: fuel injection/Motronic, cold start valve, thermo switch, and power distribution relays.
The terminal you cleaned up must have been the 2nd; if this would open intermittently the engine would definitely miss and have poor A/F mixture.

Man...in doing an electrical diag. using the manual this one would be at the later areas of an evaluation.
Jon