What do you want for a response? You have already said that sending the RCM to DJ is not really practical, agreed. You KNOW the RCM is bad, therefore, the practical move is to just buy a new one. Once you do this, if the car goes back to normal, you have final confirmation that the entire issue is the RCM.

If you buy a new RCM and still have issues, you NOW have a direction to go.

Knowing how to solder is fine, but knowing how to solder and doing electrical diagnostics (which you obviously have some skill in) are separate skills. The RCM is a simply collection of relays with a few diodes. A new RCM is not expensive, and man of us (myself included) carry a spare.

When my RCM's Engine Control relay failed, I sent it to DJ and ordered a new RCM. Got the car running on the new RCM and DJ fixed mine and now I have a spare, which we all should have. The way I see it, it is time to order a NEW RCM and then deal with the old one after that. Once you put the new RCM in and verify ALL is OK, you know that the old RCM really is the problem and that means: bad relay, open diode. open solder junction/path, etc; fixing ANY of that involves only soldering or changing a relay. I was not going to mess with it, after 20 years in bench repairs, then almost 20 more in systems, my eyes are not suitable for such work anymore.

Again, I think you are making this WAY harder than it should be. I will leave you to other contributors on here who see it your way and not mine. You asked for my time and help, I offered it and you found it insulting - fine, others will step in, you do not need me and I need not spend time with someone who gets his 'feelings' hurt when someone offers their time and experience free of charge.