Mrtennis, unfortunately I can't relate SS fatigue above 1kHz with mods and upgrades to it. There's no general rule of thumb on that, but particular to Accuphase P-300 many folks, owners would NOT suggest any upgrades and keep it as original as possible matching all values replaced circuit elements.
Your task is to find any owner of any accuphase amp that gets fatigue post 1000Hz.
I will be providing service to E202 this weekend and charged $250 for labor only having all parts provided by owner. To my knowlege the parts match ones on the circuit board. My job will include reapplying new solder(purchased by client), cleaning and reconditioning all switches and potentiometers, repairing a volume control, cleaning faceplate, replacing filter and other DC caps and cleaning all RCA sockets and binding posts. There's a shop in Long Island(NY) that would do that for $450 including all circuit elements replaced and serviced. $680 seems to be a professional rip-off.
