If your C370 problem was the protection board (zener heats the caps and kills 'em), the common fix isn't really a fix. The problem is heat is conducted through the zener leads, through the traces, and right into the caps. They don't last very long. The problem is not proximity, as is commonly thought, and moving the zener to the opposite side of the board provides little improvement. What you have to do is prevent conduction. That can be done in several ways. Space in front is limited, so I put the zener in back, but put long copper heat sinks (sheet metal strips) on the leads. In hindsight, a better solution would be to attach the copper strips to the zener pads, then solder the zener to the strips at the other end. You have to get rid of the heat before it gets into the traces on the pcb. You also have to heat sink the zener, as they rely on the leads to dissipate heat.
