Have you had the EPS electronics out, the box behind the airbag blank. I can’t remember whether the cables are hard wired in or if there’s a connector, which ever way, if you haven’t already, drop it out & look at the board. You’ve already had experience with corrosion on PCB’s so you know what you’re looking for & clean contacts with contact cleaner NOT with WD40 that stuff is the sperm of Satan in the wrong places. In my opinion the bin is the right place.
On the SRS front. You say you’ve fitted a replacement column, have you retained the original wheel? Have you looked at the clock spring & associate paraphernalia, both in the wheel & behind. Having just advised the judicious use of contact cleaner on the steering electronics, I would keep the SRS contacts dry plugging them in & out a number of times to let the contacts wipe themselves clean.
One thought “off the wall”, the replacement SRS unit you have could be configured for dual airbags, if that’s the case your light isn’t going to go out.
And if, when you’ve changed the remaining seatbelt fireworks you’ve still bogged down change the yellow loom, then make friends with someone with a Pscan.
M