I had the odd wiper issue on my 97 Hoe about 7 or so years ago. Chevy was willing at that time to re-imburse for the new board, which was a known common problem, and there was a recall issued for a good number of years. I was in the "Clouds" in Cloudcroft NM at the time, and in a rain, so it was good I was in the habit of Rain-X'ing all the glass. They were intermittent to none basically that day they failed.
After all the ******** chevy wanted to put me through, with copies of utilility bills, and a bunch of other stupid runaround BS, I decided to do some surgery myself, and said screw chevy. (and I'm glad I did, I hate dealers)
What I found was a board entirely covered in red grease, and on the worm gear where there should've been some, basically no grease at all.
After a spray down on the board with good electrical contact cleaner, I could see no evidence of any cold solder joints. (which even back then was one of the common known issues of failure)
I re-distributed basically all of the grease to the gears where I felt it should've been in the first place, I also noticed what looked to be two brass (or copper) contact wafers which were loaded with grease also. I removed much of it, leaving only just a thin coating.
I cleaned the plug connection, re-assembled, and all worked perfect. Haven't had a problem since.