I think many of the best ever cassette decks have been listed above. I followed a couple of the Sony WM professionals on ebay recently, and they went for around £120-150.
AFAIK you can still get any Nakamichi serviced by B&W. There is steady trickle of them.
A decent three-head Sony deck just went for £21. I had bid £20!
I agree with the observation that a well-kept machine is usually OK, but maybe I've been lucky. I bought my Nak in 1999 after I saw a flyer at a London hi-fi show, that the owner had cheekily left lying around. Has been briliant.