Do you have another board to test you game out with while you work on this one? Honestly if it were me I would use it as practice and count it as a bonus if I revive it. I just had a board like this recently and the reset generator change is the way to go for this sort of board. You have to ohm out all the connections and vias when you get all the cleanup and repairs done. I had 1 via in that area not making a connection and hung up the board.

Don't forget to check/replace the dipswitches while you are at it. I got a project machine a few years ago with an mpu that was "sent out for repair" and ended up having to replace them all after I noticed a bunch were not working from battery corrosion.

Its not that hard to remove the heatsink from the power board just don't rush and yank it off. When you re assemble it make sure you ohm out the connections for the transistor Q3. It may end up testing fine with continuity but still making a poor connection after you solder it back in place so testing ohms should tell you need to add jumper wires on the top side to make the connection.