Most old rangefinder is centerweighted metering, may need to compensate a lot for extreme contrast scenes to prevent under/over exposure, unlike the newer multi-segment metering in new cameras.
very inaccurate metering(if not due to reason above) i think cause by many reasons like
1. maybe cds dislodged from its proper location in the camera, need technician to refix it in proper place
2. cds cells faulty, no longer giving correct value
3. yes, calibration out, need to be adjusted
4. etc
If u do not own or intend to own a separate meter or camera is aperture priority then u will need to calibrate that meter. Then, how much u willing to spend?
I think it may cause more than $50.
You may try shop in same building as camera workshop, Camix, the small shop opposite the cafeteria.