AEG lavamat turbo 16830 door locking fault

My AEG 16830 stopped dead with 2 minutes to go on a 30 degree wash cycle, and after some delay showed an E40 fault. Diagnostics then refined the fault to E41. Some trial runs confirmed the E41 diagnosis: door not locking (although sometimes there were clicks to suggest it was trying).

I once had a similar fault before, solved by replacing the door interlock device. So I ordered one of those. When I came to install it I found that the machine’s connector plug for the interlock had two badly blackened female terminals (the ones numbered 4+5). It looks like the effect of a short. The old interlock that I removed only had a little blackness on male terminal 4 – otherwise it was superficially undamaged.

Sadly, installing the new interlock did not correct the fault. Further testing of the machine showed the fault to be erratic, even on the same programme:

– sometimes the machine attempts to operate (with clicks for the door lock) and then shows E40;
– sometimes the machine just doesn’t do anything beyond showing its lights and time to run (i.e. silent sulking);
-sometimes the machine starts (and appears to lock), fills, and then hangs (with no error message) at some point during the wash. Then it just sits at 14 mins, or whatever, and I have to turn it off and drain it manually.

I made a point of disconnecting the electricity supply to the machine and leaving it for a few minutes between all test runs to make sure that any previous error states were cleared.

Thinking out loud here, but one hypothesis is a loose connection caused by oxidising of those blackened female terminals on the connector. Hard to get at them to clean them up. But the blackened terminals may themselves be a symptom of another problem. One possible cause of a short would be a small tear that I spotted (1 cm) in the folds of the rubber door seal, fairly high up on the lock side, that might (I suppose) have allowed a splash to reach the interlock connector. But no sign of moisture nearby, only a bit of dust, so maybe that’s a red herring.

So perhaps the blackened terminals point to something further back in the machine’s electronics. Am I right in thinking that the next component back from the interlock is a microswitch, before we reach the main circuit board? Is there any point in replacing the microswitch, do you think? Or is that an all-or-nothing component that wouldn’t explain the erratic behaviour listed above? It seems unlikely to me that a fault in the main board itself would be a more likely explanation for such erratic behaviour but I’m open to being put right by someone who knows!

Anyway, I am looking for advice on what would explain the fault, and in particular what might be a good next step. Many thanks!