Did you try cleaning their face with acetone then wiping on some heatsink compound, then wiping it off with a dry cloth? That generally makes virtually every face readable.
Yes. I remember the service manual. That service manual is nearly in the class of the old Tektronix service manuals. Those old manuals and scopes were a work of art.
Not going to change gate resistors, I see none. goes straight to the drivers, off the gate pads- D40D8 (obsolete) and a MPSa56. It does however have a 100 ohm resistor from driver to the 594.