Restoring Reel to Reel Audio 

As you discovered, playing the tape on another recorder that works is a good solution. And tapes made on small, cheap portable recorders like the Sanyo will usually require speed correction to sound right, which is best done in the computer. I've done tape transfers like this professionally for many years. You did good.

Don't know if you knew already, but the American version of that Sanyo device (or a very similar one, under the Craig brand) was frequently used in the mission briefings for the original Mission: Impossible show. They removed the cover to make it look cooler, but it's the same underneath.

You could probably find new belts for it