The most common surprise is a bent track that's been masking the real problem - the door seemed to run rough because of the rollers, but once they're replaced the door still binds because the track rail itself warped where the old roller was dragging. That's a separate repair, not included in a roller swap, and we'll flag it before doing the work rather than after. The other thing worth knowing: on a handful of doors this old, the hinges themselves are worn enough that a new roller won't sit right in the stem hole, and the hinge needs replacing alongside the roller. We'll tell you straight if that's the case - it's a small added cost, but skipping it means the new roller wears out again within a year.