Several years ago, during a bench check of one of my KTR-900A's the tech noted several older discolored components, and replaced these rather than leave them in.
Now of course, the new ones could have failed right away, but they of course, did not.
I firmly believe that with older avionics, a bench check from time to time will prevent (or help to prevent) an AOG condition, and resultant out of base expense.
I would much rather pay a little now rather than a lot (as in, inconvenience) later.
You pays your money...takes your chances.
And then we come to the discussion of glass, and the possible retro-fit in older aircraft.
Three years ago, the local owner of a Lockheed JetStar decided to replace his steam gauges with glass, and also the older Collins avionics as well.
The techs cut all the old wiring harnesses out and proceeded to install all the new boxes, instruments, etc.
When it was all completed, it sure did look nice, but strangely enough, it didn't work all that well in flight.
So poorly in fact, that the FAA would not certify the installation.
So, the new boxes went out and the old back in...with new harnesses from Lockheed, which still supports the JetStar, oddly enough.