Door lock controller?

[SatRoc]

My '04 E320 Wagon has suffered from this problem since I purchased her a few months back. If you're in the car the switches to lock and unlock the doors work great. If you shut the car down and try to lock her with the key fob, sometimes it works, sometimes it doesn't. Bought a new key fob, same result. All batteries are new. When the key fob works, you can unlock the car with it immediately but if you wait a few hours, it won't work. I'm not an EE, but it appears to me that there might be a capacitor somewhere that isn't holding a charge.

What I'm really looking for is a schematic of the circuit controlling the IR functions for the door locks or, if by chance someone has suffered with this problem, the solution .

Thank you in advance.