Issues With GRE PSR-500 And 600s

I have a GRE PSR-500 and 600 radios that both seem to have lost sensitivity over the years. I have a Whistler TRX-1 handheld with a rubber duck antenna seems to have far more sensitivity when placed side by side. I also have a Whistler WS-1065 that seems to have developed the same loss of sensitivity. Has anyone else dealt with this issue and have an idea of what the cause is? I would sure like to have my older radios fixed