I had a EE friend repair mine and do a rebuild of them. He checked re-soldered many of the diodes as the solder joints were broken. Replaced many of the caps and added good quality point to point wiring instead of using the traces on the printed board. Changed the speaker binding posts to gold and replaced the fuse holder with a gold plated one. The power supplies were fine so they were left alone.
I'm sure I posted it in my equipment threat. Take a look there and I will also look this weekend for it. I included at least one picture of what it looked like when finished.
The improvement was not subtle. Even more open with more detail. My panels would have been probably 8 years old at that time.