remote key pad lock/unlock intermittent

Here's the problem on my 98 explorer xlt - The remote key pad works to unlock or lock, but the button has to be pushed 7 or 8 times. Sometimes more sometimes less. I also have to be right next to the vehicle, it used to work first time, everytime even at say 20 feet away. I broke out the spare fob thinking I worn out the one I'd been using, same problem. I replaced the batteries, still the same problem. I also checked the old and new batteries with a voltmeter, thinking I might have bought bad batteries - the batteries were good. The dealer tried another keypad and same problem. Both of my key pads have been reprogrammed and still the same problem.
One thing that does work better - with the case apart and pressing the contacts they seem to work the first time. I've added a small strip of plastic to help make firmer contact, but it only helped a little. It seems unlikely that the spare that's only been used 4-5 times in 7 years would be worn that much though.
Any suggestions would be greatly appreciated.

Sounds like your receiver may be on its way out. It happens in older Taurus models all the time, I can't imagine the Explorer would be any different as far as the receiver goes.