If you decide to ship it, Willie Herman would probably be your best bet. He's probably one of the top Nakamichi techs in the country.
In addition to Willie Herman (for my Nak Dragon) I've used Russel from New Jersey Factory Service to keep my R2R tape deck in tip top condition over the years. Good, reasonable and fast. He's in Emerson, NJ. 201-967-0060
Willie Herman is THE Nakamichi repair guru if you want to ship. But be prepared to pay.
I would agree with ALL of the above posts.
It really has to be Willie Herman.
I have owned a Hermanised 582 and now a ZX7.
However you get what you pay for and expect a bit of a wait, his reputation is earned .
Depending what it needs you are likely to be looking at $500 to $800 plus BUT that should last you a lifetime.
I have a reference Hot Tuna Acoustic Live tape recorded on TDK SA on my zx7 that is simply out of this world and should convince any naysayers on the potential of cassette tape SQ.
Good luck and welcome to the wacky world of Nak decks but you probably have the best consumer deck in your hands right now.
How deep is your pocket?
Besides the normal run of the mill cap upgrades there is not much more a good zx7 needs Tbh.
However check out their website for options and contact info.
cleeds,NJ Factory Service has a good reputation and I don't wish to sully it here. Over time, any business will have a few disappointed customers and I'm one of theirs. Suffice it to say I have no reason to do business with them again.