Very sorry about the delay in getting back to this, all. Been sick as a dog for a while.
At the last annual, I had brand-new Slick mags installed (the old Bendix ones were coming up for the 500-hour inspection that costs almost as much as the replacements). I doubt it's a mag problem, then.
When the engine is stopped, though, the airscrew is in the vertical position: straight up, straight down. I take it that that's not where it ought to be?