There was a Technical Service Bulletin and a parts counter fixer upper kit.

The parts went inside the motor housing and maybe had something to do with the reverse/park circuit and mechanicals.

Sorry, can't remember if this TSB and kit was for a parking problem or a non-operating problem. I installed the kit in my Barracuda in the early 70s.

If you need a 68 FSM/wiring schematic, PM me. You could jumper 12v directly to the motor without the switch, guided by the schematics. This would tell you if the motor works by itself skipping the switch. The schematic shows 4 wires for both variable speed and 2-speed wipers, brown, red, dark green, and dark blue in the engine compartment, but you will have to correlate this to the instrument panel schematic and switch to see which wire(s) you need to jumper.