Keyring Remote Lock/Unlock device

 When I bought my 95 GMC Savana Van, I had the dealer install a remote starter. The keyring control was supposed to lock and unlock all the doors too. Never did! From the gitgo... it has worked on all the doors except the drivers door! That one only will remotely unlock occasionally when it's raining, or cold and snowy. The original factory keyring control works fine though, and always has. 

The GM service manager told me that I’d just have to use both controls. Later when I protested and said I’d like them to make good on the installation, I was told that too much time had elapsed and it would cost me perhaps $150 or so. Of course I refused.

Can you suggest what might be going on, and is there anything that I can do to set things right, other than spray painting graffiti on the Service Bay doors?

Thanks very much and Thanks too for Car Talk and all the smiles… Roger