Most jobs on a door from this era start the same way - check spring tension, check the drums and cables for wear consistent with 40-plus years of cycles, then look at the rollers and hinges before touching the opener at all. If the door is original to a house built around 1981, we're often replacing more than the part that failed, simply because everything else on the door is the same age and close behind it.
On the opener, if it's an older chain-drive unit, we'll tell you straight whether it's worth repairing or whether a belt-drive replacement makes more sense long term - that call depends on what's actually broken, not on upselling. We finish every job with a manual balance check, since a door that opens fine on a working opener can still be dangerously out of balance underneath.