Over the past year I have returned 8 cannibalized MEP 003A generators to good working condition, but I am the first to admit I am no expert. I had several with inoperative or screwy reading Hz meters. In every case I got them reading accurately by removing the transducer and adjusting the two "pots" just under the resin potting goo. The goo in each of my transducers was very easily scraped away.
Proceed the next steps carefully. You will be using 120VAC to calibrate your transducer. The transducer is designed to take 120VAC and convert it to DC which operates the Hz meter which in nothing more than a DC milli-amp meter.
To calibrate my transducers I connected 120VAC from a typical house AC outlet to the two INPUT terminals of the transducer. I use a GFCI protected cord I cut off a defunct hair dryer with alligator clips on the end of each wire. I connected the Hz meter to the two OUTPUT terminals on the transducer. I carefully turned one or the other of the two adjustment pots until the Hz meter read exactly 60 Hz. I do not remember which pot I turned, I think one pot sets the "span" and the other one sets the center accuracy. When I installed the transducers and the Hz meters back in the generators, they all worked perfectly.
Your results may vary.