Pulled the box out today, all but down to a fine art these days haha.

Hasn't stripped splines off 5th but instead has pushed the circlip off the end of the countershaft and with it the engaging gear. New bearings and upgraded mainshaft along with new selector detents and 1st/2nd fork it should be right to rock.

Also found the source of my whine, front counter bearing had gone through hardening so it would have faily at some point.