first thing to do is remove the head block and send off to JRF for inspection.
Really depends on the age and model. The MTRs are getting old enough a recap of at least the power supply may be good.
On the MX 5050s there was a mk1, mk2 and mk3. The latest mk3 may only need a head inspection, oil the capstan motor and pinch roller and clean a few pots.
The earlier models may need a bit more.
In the Pacific NW Reeltoreeltech.com is quite good.

