I had a ST140 rebuilt about 1 1/2 years ago. Mine was the later vintage (1993) unit that was the immediate predecessor to the ST1400, heat sinks inside, same parts essentially as the ST1400. When I called them to set it up they said the output transistors were no longer available and in order to rebuid it they would have to replace them all (ie rather than just the bad ones I had one channel gone). It turned out that mine already had the later vintage outputs so I wasn't in that boat, but if yours is the original 80's model I assume the issue is with the outputs, and I doubt you'll want to pay the money to replace them. You can instead buy a used ST140 for less.
As far as general service, are you sure they will not touch it? I sent my M200 monoblock in last year (80's vintage - outputs not available either) and they did a complete tuneup. This amounted to full checkup, replacing the power stitch, set bias, replace all the fuses. $50 for the service, plus shipping. If it needed a resistor, or cap, or some basic part like that I believe they would have installed it.
Other than that, I imagine you can find any one of a number of techs who will service it.