I just went through this on an M104, same tensioner assembly as the M103. The pully is obvious, if the bearing is smooth/tight/quiet, and the dust cover is still on the front of it, you're probably fine.

The spring on the other hand, has been a pain for me. Mine wasn't tensioning the belt, beyond the limit of the adjuster nut. I removed it and compared the orientation of the flats to the photos on several (Worldparts supplied photo) parts suppliers' sites, same photo, showed the flats generally in an orientation where the plane would pass between the two ears on the tensioner. Mine is roughly 90degrees to that (click on buy parts above to see what I mean). In a pinch, a weekend, I removed one from a parts M103, found it to be in about the same orientation, but better by several degrees, and it tensioned the belt properly. Both tensioners had good spring force when the flats were clamped in a vice and tensioner rotated.

In summary; I don't think that you can tell without installing it or comparing it to a known good one.

__________________

Gone to the dark side

- Jeff