Once the box is apart there is an abvious strip of metal which contact the other side. I used fine sandpaper to clean this contact strip, and the other side where it contacts

Hi Andy,

I'm curious about this too see earlier post. I think the "box" as you call it is the "Ignition Amplifier" built into a heatsink. If so, it would compare to the Bosch "Power Stage", which is known to overheat when the "thermal grease" between its heatsink and body metal dries out after many years—reducing or blocking the needed heat dissipation to the body.

I also think this heat-related failure can be intermittent (coming on after X hours of running) or solid, and that there was a recent post where the REX ignition responded to a refreshing of that thermal grease. But so far I haven't removed the "box" myself to see what that "contact strip" looks like. I believe it's more than a ground contact (if that), and is more for heat transfer. If so, it probably would benefit from something like Radio Shack's "Heatsink Grease".

I'll be taking mine more fully apart soon to see for myself, in any case.
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.