Need Diagnosis, remote door lock.

[amqaap]

1994 roadmaster with 70,000 miles. Both remotes stopped working at the same time. The batteries were replaced 18 months ago and all were 3+ volts. All fuses checked out good. The power locks are fine when operated from inside the car. At the same time that the batteries died, the locks started to intmtly self cycle while the headlights were on. Local independent garage looked at it for a day and said it way above his capability (no charge) Took it to a Buick dealer (big charge), Inspected harness for shorts, inspected connectors, repaired circuit 1940 due to shorting, replaced door lock module in rear dash, reprogrammed remotes, put new batteries in remotes had the car for two weeks and could not dupicate the problem anymore. Pronounced it fixed. I drove the car 20 feet and the the only thing that had changed was that one remote was working. Dealer was shocked, and still has car with no idea as to what is causing problem Any ideas? help!