NAK 670ZX play problem, an easy fix?

Hello, everyone. It looks like I may have gotten burned on a Nakamichi 670ZX cassette deck I bought on eBay. The unit had been represented to me as working for the previous owner, as recently as last September. I tested the unit upon its arrival to discover that the Play function is not working. FF , Pause, RW, and VU meters seem OK. However, the Play runs the tape at a very high speed when played from the beginning of the tape. As the tape progresses, the Play speeds up and slows down in ever-widening whirring spurts. When the middle of the tape is reached, the tape simply shifts to Stop mode. Also, a brief whirring, squeaking mechanical noise comes from inside the deck when the tape is manually stopped at any point in the play and also when it stops by itself . I'm not a tech, so I'm anticipating this could be a costly and prohibitive repair, unless it's a simple and quick fix I can do myself. Does anyone out there have any familiarity with this type of problem and this deck? Comments and suggestions will be appreciated. Thanks.