Vibration could be a big factor. The first time I inspected the control box there was a rattling. The pcb was loose inside. I gently checked it , including light pressing of the chip (looked like eprom) before hot melt gluing it back. It worked for a while but more vibrations could well have caused the poor joints I eventually found, to fail. The box was screwed to the ash frame behind the dash. Maybe I should have put some vibration damping in ...rubber/neoprene. No problems since though.
