Haven't measured an MC18 in an age, but I'm pretty sure that the pot is 5ohms just like the MC21, MC28 and NSR150.

For your info, the TPS is also a 5ohm pot.

Wiring in a later model servo should be a breeze. Just check the wire colours carefully and match them up. They all do the same thing.

Maybe also run the engine with the RC valve actuation cables disconnected just to make sure that the servo is doping what it should.

I've saved a couple of TPS pots before by throwing them in the ultrasonic cleaner, but never done an RC servo pot. Never needed to.

Cheers,

Matt.