There are two types of tape decks, ones that are broken and ones that will be broken. I swore off servicing them years ago unless they are really worth it (and the client wants to pay for it).
Believe it or not, the Nakamichi’s are surprisingly strait forward to disassemble replace belts and service- just don’t touch anything in regards to biasing- special equipment is needed and few people left on the planet who have the equipment and know how to use it. I have always found that if the deck is still set to factory specs, just leave them alone. If they sound funky, usually a head cleaning and demag do the trick.
Tascam decks are also worth servicing, as are the upper end Denon.