The auto side of the interior lights is driven by the security controller. If my experience is anything to go by, the previous owner has probably blown this output on the security system and hence no more auto interior lights.
My solution was to run a relay driven off the doors input (all 5 doors go to the one input) to the security system, this relay then drives the auto function of the interior lights.
Cheers Glen
NB, don't muck about with the green stuff, just cut it off. Take a look at the wires cause it can start to creep up those to. It's exactly like rust, if you leave the smallest amount it will self propagate.
From memory, white vinegar will start the job of cleaning the green stuff up. Electrical cleaner is usually isopropyl which is great for dirt and gum and it dries quickly, but it won't do too much for corrosion.

