2004 e150 sport - problem w/ door locks

[manofage]

Initially, the remote door locks began functioning sporadically. They still worked perfectly from the inside switches. Problem has worsened and the remote system no longer works at all. I've changed the batteries in the remote, no go.
Took it to a dealer for a diagnosis. He insisted on changing the batteries in the two remote sending units (which I'd already done myself) and confirmed proper functioning of the senders. He was unable to diagnose the problem beyond that, but kept me waiting for two hours while he came up with all sorts of unrelated repairs he wanted to do on my van. He refused to give me any estimate on what it might cost to replace the apparent source of the problem which, in my estimation, is the receiver unit. I'm also not sure where in the van the unit is located, and the man at the dealership could neither tell me this nor what the proper name (for this receiving unit) is.

Any help would be appreciated.