As I indicated in another post, I'm rebuilding my T5.  It has been whining so I figured it was bearings.  One contributing factor may have been some galling on the mainshaft pilot bearing area.  So I took it to Texas Driveline Performance (https://www.texasdrivetrainperformance.com/).  They have a guy there who mounts mainshafts in a custom lathe that spins at a slow rpm for welding.  They use a special air hardening rod to weld up the bearing surface.  Jason the owner told me the Rockwell hardness is correct without having to heat treat it. After welding they mount it to another lathe and grind it to spec.  Below are the before and after pics.  Cost was $50.  Very impressed.  They get a lot of transmission mainshafts from around the country, so if you need any kind of bearing surface repaired you may wish to give them a call.