Help with an EQ6 rebuild

[rnobleeddy]

I have an old, old EQ6. Provenance unknown, it's black with the words "Heavy Duty" on it.  But it's been guiding at about 0.8" RMS for the last year, so I decided to belt mod it. It didn't really want to come apart, but with a lot of tapping out of bearings what were stuck on shafts, I eventually dissembled it.

The problem I face now is that the large, cylindrical brass worm gear won't fit back in the mount. 

Whereas in the various guides and on the attached video (~3m 50s in), the RA axis just slots back on the mount, for me, the brass cylindrical gearing won't even fit back in the mount. I've taken a short video showing just the brass section not fitting in the mount - https://photos.app.goo.gl/XiXf9tHPEPWxuH528. I'd previously fitted the RA axis with a little tapping, but it was locked solid, only moving when the worm drive was engaged.

The RA axis was previously stiff, but did move. 

Aside from the obvious approach of sanding/smoothing, am I missing something obvious? It's hard to understand how the RA axis used to rotate, but now won't even fit together:?