It would a pity to put aside such a good old (robust, basic) unit.
You're saying it's "just outside its limits for power outputs" ... how do (did) you measure those?
And (or) ... does the front panel output indicator match measured output?
Anyway, don't start tweaking pots. Assuming you have taken the lid off - any sign of "deterioration" (brown marks - "stressed" or failed components)?
If the output is really low, maybe the output transistors are getting a bit tired. One could even be out of play (failed) altogether.
How do things (waveforms) look on a 'scope?