Did the problem begin at the same time with the two motors? If so there might be some kind of cross-connection in the wiring creating an overheating issue requiring the circuit breakers or fuse to trip/blow.
I would check all the ground connections as well as connections to the fuse box. After so many years the connections could be corroded making for overheating of the wires.
The motors themselves might need overhauled...maybe the wiring harness itself has become suspect and required replacing.