That is the rather rare "big button" drive. Be very hard finding a replacement. No belt, the main motor is run by a ring of electromagnets under that big disc of metal on the underside. Does the disc spin when the drive starts up? The Sankyo motor looks like a stepper for the head carriage.
I have a small button drive that has the same problem. It cannot find Track 0, although you can see it moving the head and trying, so I think like yours the head movement is OK. One thing to try is to demagnetise the heads. There are various ways to do it - the best is with a tape head demagnetiser, which is just an electromagnet with a probe on the end, connected to the mains (AC). The moving magnetic field is concentrated at the tip, and it is this that removes any residual magnetism from the head. You just need to hold it on the head for a while.
Let us know how you get on.
Too many retro computers here: 1040STfm, Mega4, Ultrasatanx2 , Amiga A500, A500+ and A1200, Acorn Atom x2, BBC Micro, Electron, Spectrum 48k x2, +48, +128k, QL, Oric Atmos, ZX81, Memotech MTX512, Amstrad 6128 x2..