Footwell full of water is usually the seam sealer failure under the bonnet. Sometimes soaks the BCM and causes all sort of issues. Got a lovely low mile Corsa C for my daughter in 2012 for £300 that was a non runner with a loss of comms to ECU fault. Bought a complete ECU set up (ECU, clocks, transponder, keys etc for £170 ish. Fitted it all, made no difference. Found someone had power probed the main ECU cable in the loom and it went green and rotted out. Soldered in a short piece and fixed it. Still have the clocks and ECU here which was removed!
Urrggg I assume you mean they had pierced the wire for testing then not re-sealed it.
I followed behind someone else's inconclusive diag session a week back. I think it was done by Edward Scissorhands ! (Yes, I fixed it - failed fuel pump relay... on a running car..took me a while)