I've not had or recall hearing here about one of these rear wiper motor assemblies failing. If it was a 240 front wiper motor then I'd have all kinds of ideas as they were indeed troublesome, also repairable. Could be something like the copper contact fingers in the gearcase for the park and wipe function giving up. If the case is rivetted then disassembly for inspection and possible repair is going to be difficult. I'm not sure I'd even bother, just start shopping around for a good used one.

That's one weird looking resistor, looks more like a diode. Oh, wait, the wiring diagram indeed shows a protective diode in the motor on the "31b" terminal. That could easily be the problem. You'd have to take one end out of circuit to test it for directional resistance to see if it's failed (in the park position the contact in the motor is parallel to it and will give near zero resistance if measured in circuit). Shouldn't be too hard to replace it, either soldered (careful with the heat) or using a crimp ferrel. Just find a 12V rated diode of suitably high watts (which should be the number before the W I see, a higher wattage would be okay too) and there's a good chance you might be able to repair it. [edit: ignore my previous comments about the possibility of it being a capacitor]

Only problems I've had with those wipers is the spring in the arms getting weaker over time and in one wagon the nut on the threaded aluminum collar through the gate continually works loose so the wiper wobbles. I'm thinking it initially became slightly loose and over time the threads have become damaged. I'm just about ready to JB Weld it in place next time I've got the panel off. 13" wiper blades are also not that easy to find so I just cut down old front wiper blades and insert them in the holder.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now