If your using old tapes, they could be stretched or warped. If they're new tapes, though, anything up to a C90 should be fine (the 120s should definitely be avoided at all costs, though.)
Get a new C60 for testing. Stick with Maxell if you can, and go with high-bias chrome; go with metal for now
only if that's all the machine will take, otherwise stick with chrome for the testing. Clean the heads, capstan and pinch roller with quality head cleaning fluid (stay away from drugstore rubbing alchohol) and lint-free swabs (no Q-Tip brand swabs.) Clean these parts by rubbing only in the direction of tape travel (left-right, not up-down).
After cleaning inspect the heads and the pinch roller carefully, If you still see "rust bands" where the tape path is and/or you see an indentation in the pinch roller where the tape travels, you have severe tape path wear. If the rubber on the capstan or pinch roller appear cracked anywhere, they need replacing.
If they look OK to the eyesight, then try the new tape. If you're still getting wow, you probably either have a deformed or worn capstan, pinch roller or pinch roller spindle, or you have a worn or stretched drive belt. If after all those have been checked or passed, then it's most likely a worn out drive motor itself.
Good luck. Hope it's only the tape
.
G.
