Question regarding older phono preamp

No denying what Mijo says, but older solid state gear also have issues, such as transistors or especially ICs and op amps that are simply no longer available. Furthermore, a tube circuit can usually be traced out in the absence of a schematic. Whereas that’s much more difficult with SS. Older SS gear typically used a lot of electrolytic capacitors as well.

Electrolytic capacitors fail over time. No matter what. But lack of use is worst case. if your unit was in storage for more than 10 years, you might have someone check the power supply caps. Film capacitors do last essentially forever, unless they have seen a voltage that exceeds their rated maximum voltage. In general, if your unit sounds OK, the capacitors are probably OK. Among resistors, carbon composition resistors (brown cylinders with colored banding) change value over time. In certain cases, this can throw the circuit out of whack and cause poor sound quality or even damage other components. They rarely fail completely, but they do change value over time.