As for the rear door lock, they work on a vaccum. you might have avacuum leak on that door. you will probably have to pull the panel, unless it is just something sticky in the lock, in which case you will probably need to pull the panel anyway. be carefull, and get a panel popping tool.
As for the Map lights, the cover should pop out some how.
for the seat switch lights, you can probably do it without removing the panel, but I am not sure on this either.
It is a place to start though, check for an escaping air sound when you lock and unlock the car on that door.
I'm not a tech, but I hope that helps you find a place to start.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.