On the older stock, the common failure is a torsion spring that's simply worn out from three to four decades of cycles, or hinges and rollers that have never been replaced and are starting to bind the track. Parts for these are still available, but not always off the shelf at every supplier, so a same-visit fix isn't guaranteed if the spring size is uncommon.
On houses built later in the range, we see lighter panels that dent more easily and extension spring setups that are simpler to service but wear their safety cables faster. Neither era is better or worse to own, they just fail differently, and knowing which one you've got before the truck arrives saves time on the call.
One honest limit: if a door's track is badly rusted or the panels are cracked clean through, we're not going to push a spring replacement that leaves you with a door still failing somewhere else. Sometimes the repair isn't worth doing and we'll say so.