Accuphase P-300, worth upgrading?

I recently acquired an Accuphase P-300 power amp and my question is about rebuilding it. I haven't really listened to it yet, other than hooking it up to see if it worked and it seems fine. The amp is in mint condition but it is close to 40 years old so I am sure it needs serviced and I would like to upgrade it to sound as good as it can, if that is practical. If I were to refurbish this amp just how good can it be? What price range in a current amp would it compare to? I have $600 in the amp. Who would you send it to to bring it up to speed? Any thoughts or suggestions are very much appreciated.