The gear is part of X-3363-501-1 motor assembly. It is attached to reel motor shaft. The gear can tend to crack during the time and tape drive can become more noisy or does not work correctly.
Faulty gear can be replaced with 3D printed one. This type of drive mechanism is quite easy to disassembly – just follow service guide steps. You can find the gear here in schematics:
Here is video showing replacement of the gear and operation in drive mechanism.
Gear is compatible with following Sony devices:
MHC160, MHC1600, HS-TD107R, DX-AC90, TC-W490, TC-WR531, TC-WR545, TC-WR565, TC-WR645S, TC-H1600, TC-WR665S, TC-W435, TC-WE405, TC-WR635S, TC-WR701ES, TC-WR735S, TC-WE835S, TC-WA8ESA, TC-KA1ESA, DX-AS70C, HS-TD30, HS-TD305, TC-H3600, TC-W411, TC-WE625, TC-WE825S, TC-WR520, TC-WR570, TC-WR62, TC-WR620, TC-WR720, TC-WR720A, TC-WR820A, TC-WE725.
However, it might work also with other devices – just check your service manual.
This gear can also replace X-3363-501-2, that is exactly the same.
Available for purchase – go to shop.