I recently bought a '95 DeVille Concours. I put a new battery in the keyless transmitter, but it still doesn't work. Cadillac.com said to check my user manual on how to "resynchronize the transmitter after changing the battery"; but my manual contains no such instructions.
Note: Before starting this procedure, BOTH transmitters must be present. Failure to use both transmitters will render the RKE system inoperative.(If the customer uses only one transmitter on the vehicle, use this transmitter as transmitter 1 and 2; which is not the normal situation). The entire reprogramming sequence must be completed within 30 seconds of grounding the reprogramming connector [Step 1 and 2 below]. If the procedure is not completed, remove the ground at the connector and restart the procedure from step  one.
Ground black single wire connector located at trunk pull down unit.
Wait for door locks to lock and unlock [a few seconds]
Press the UNLOCK button on the first transmitter twice. Pause for one second between presses.
Wait for door locks to lock and unlock. [a couple of seconds]
Press the UNLOCK button on the second transmitter twice. Pause for one second between presses.
Wait for door locks to lock and unlock. About two seconds.
Remove ground from black connector.
After procedure, check to see if both transmitters operate the door locks. Repeat programming procedure or replace transmitters as necessary.
I highly doubt that the manifold is rusting, maybe you are seeing something else. The manifold is made of aluminum, to my knowledge.
Other than that, those arent anything to worry about. Maybe that "bar" that you said, sand it down and spray some rustoleum (Make sure you get high temp kind, like for bbq grills). You can always take some steel wool to it, and that will take care of it!!!