I have a gear oil leak where the speedometer cable meets the housing on the transmission. I ordered the seal (9958-60-8166) and O-ring (1011-17-443), but neither seems to be the correct size. I thought it was a weird 79-80 thing, but the part numbers are listed for pretty much all RX7s and even Miatas.

This first picture has the old O-ring and seal on the left, as well as the bore the seal installs into.

I've sourced the correct O-rings from McMaster and I've found an SKF seal that will replace the old one. Mostly I'm just curious as to what's going on here.

 

Is yours the OEM transmission? Looks like the oring expanded and the seal completely deteriorated. Are you sure the new parts will not work?

 

Maybe an older rx transmission? It is a 5 speed and attaches to a 79 drive shaft for certain, though. The old seal looks like that because of the removal. It was mostly intact but leaking before I got to it.

The sealing dimensions OD and ID are not even close on the seal, and you can see the size difference in the picture as well as the fit of the new OEM o ring in the second picture. No chance that o ring seals.