If the amp was always working for all these years than most likely you'll need to worry. Otherwise I would check/recap the amp especially electrolytic caps. They're most-likely dry and need to be checked with either cap tester or C-meter for the specified parameters. Each of these caps may cost around a dime(no need to shop for the 'improved ones' the originals are the ones the preamp is specked out for) at parts retailers and would extend the life of your unit by another decade or more.
That would require knowlege of testing and replacing electrolytic capacitors from the circuit board. Giving the unit to the local tech would hit your pocket much harder if you figure...
That would require knowlege of testing and replacing electrolytic capacitors from the circuit board. Giving the unit to the local tech would hit your pocket much harder if you figure...