See the link below. Almost all older Naks have some sort of drive problems.
You're not the only one.. I had a similiar experience purchasing a CR-3A for a very low price on ebay.. worked for about a month and then the drive quit. I gave it away.
On many units you have to do the "gear drive upgrade" and that will fix the drive problems.. I had this done to my BX-300, and my Special Edition Cassette Deck One (bought here on 'gon) already has the gear drive and has had no problems. Good luck finding someone who can perform the operation or try Electronics Service Labs in CT (but I hear they're not cheap).