When mine went out I started a couple of email dialogs with various unit rebuild shops - they all consistently said that this particular unit could not be rebuilt and even admitted to trying different things on occasion. Seems that Bosch wanted to make sure that this one was unrebuildable and used materials that would prevent it from being so - your observations reinforce that statement.

Since the light comes on for various reasons, fed back by sensors, it could be that you are very close to the tolerances that cause the error - meaning that if the sensor is detecting a change in amperage (or whatever it's checking for, fluid pressure, etc), your unit might be on the verge - over time it slips back into acceptable range so the light goes off - just a theory.

The check lights tend to reset after x number or restarts (I believe it's 30) as it only keeps x number of rows of information - eventually the oldest code drops off, so at some point your light would go off anyway, then come back on when the sensors detect the problem again.

-- John