I think the point is .. when you do the cam cover gaskets you have to lift the tray/loom out of the way, I remove the tray completely and tie the loom up out of the way .. you didn't .. THEREFORE it is POSSIBLE that you have s-t-r-e-c-h-e-d the cables inside the tray so causing damage. The fact that the bindings at the end "look good" is of little proof.
When I had an insurance repair done to my rear bumper, it would appear that they never fully disconnected the reversing sensors when they took off the bumper .... it was a few weeks later that i started to get problems, and took over three months of faffing to solve .. although the cables all LOOKED good, somewhere in there was a stretch break that was intermittent, and caused varying voltages/currents, such that eventually 3 out of 4 sensors also failed.
A new loom (and sensors) fixed it instantly ... even though I had examined the loom meticulously.
MY advice, at this stage .. bite the bullet, take the tray apart and examine the internal loom as best you can.
A mate of mine had a 2.5 V6 some years back where that loom melted due to a short, it cost him a lot of time and money to fix, as he was unable to "prove" it was caused by the Vx garage who serviced it - including cam covers - just 3 months before....... and this sounds very similar to his problems ..
