why do you look at these things ? I mean, heads for Nak decks. You have Studers, that's real tape machines.I put myself through engineering and technical school working on consumer electronics. So I've worked on plenty of cassette machines including Naks. I worked on a 700 recently for a friend and it had exactly that bad recording head problem. For my own self, there's no way I'd buy a 3-head machine because replacement record heads can be very rare and expensive, regardless of the brand. OTOH you can find good heads for 2-head machines with ease.
Nak made a number of 2-head machines that were quite nice. Not saying they sound the best but the differences are slight; if you want the best Nak, just be aware that the record head can be a problem!