Yes, the replacement STK463 is not expensive (if it works).
But I think just fixing like that, it will broke very soon after.
To fix it and make it work for a long time, I will have to check all the caps for ESR (I do not have the tool at the moment), check each resistance and after replacing all that will take way too much time, for what it is worth. I will just put it a side for the moment.
RE: Repairing or Hacking a Vintage Amp ?