Consider first replacing the pinch roller anyway. you can replace the pinch roller for another suitable or you can replace just the rubber of the pinch roller like I did.
Here I paste a previous message from mine:
I received it weeks ago. Tapes only played without audible wow and flutter up to ten or fifteen minutes. And it stoped completely about 40 minutes (for a 60 min tapes). I tried hard to clean the pinch rollers, but they were definetively worn out and hardened. So I decided to try the following.
I took a pinch roller from a broken, very cheap portable radio-cassette. As the axis of the pinch roller is bigger in the Revox, I couldn't just simply replace one of them. With one little screw driver and my fingers I took out the black rubber. I tried to do the same on the old revox pinch roller. But It was worn out and I had to remove it with a little knife, cutting and scraching it. Then, I made a lot of pressure to get the metallic central part of the pinch roller to get inside the hole of the good rubber. This way I rebuild the pinch roller.
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About the motor... first get pinch rollers working and then you probably will set the speed fine again.
Peace