You are in good hands already Brian. Those sound/speech boards aren't an easy fix when there is a problem with them. I would like to add a few things which are easy to check.

- Are the speakers still okay? In our Mars God of War one of the speakers had a burned coil causing similar issues due to overlaoding the audio amp. Their resistance should be around 8 Ohms each.

- Replace the 47nF input capacitors for the LM379S audio amp. Any DC level at the input might saturate the amp. It is a $1 fix, if it doesn't change anything it is not a great loss. When I am servicing those boards I Always replace the tantalum cap C37 for a fresh one.

- There are a few High Ohm resistors around the LM379 (R18, R21). Sometimes, you see the brownish compound resistors over there which can run out of their specifications over the years. An easy check with a multimeter.

- OpAmp U22 (741) might be a cause also; you can give it a treatment with Freeze Spray like Ed suggested already.

Although the problem is probably somewhere in the analog section......if you want to run a testrom at your sound speech board to check the digital part, send me a PM.

Good luck!

Marco