H-D Poly Oil$3.95 US for 2oz. at a dealer.
This is the number one hit. Bikes have the same problem, too. Their rear sprockets are chromed steel as well.
Tried the W-D 40 and it did work. I do remember about the water displacement aspect. I'm good with that as my first 100 yards are on a dirt road with water filled holes I have to drive through to get to asphalt.
The poly oil is a dealer only product so online shopping is a bit of a pain.
At least I think this is going in the right direction!
A further note from the bike forums: The belts will last 100,000 miles with minimal grief. The people who are breaking them are racing with high hp motors pushing 200hp at the rear. Ours are seeing 85-100 depending on the literature, just like most big bikes. The belt is far tougher than the rear sprocket.