Just checking in on this OEM door lock modification and refurbishment thread. Can't believe it's been almost 7 years, but I'm happy to report that the system has worked flawlessly ever since.
Also, I didn't see this last post, so I'll respond for posterity:
Actually, in my case it was indeed water intrusion that caused the burning in the solenoid. I know this because there was evidence by way of water staining in the inside bottom of the cylinder case where water pooled, and a trace where the water came in through the case seam. In addition, my relays were in pristine condition and passed testing, so much so that I saved them as spares.
Over the years since I did this project, the car was caught in torrential Florida rain a few times, and thankfully the silicone RTV seam I added prevented a recurrence.