I know that feeling!
The FSR helped about 80%, but I had to leave it on for about 30 minutes. It was a cool, damp day, though and that might have diluted it some. The rest pretty much came off with compound and elbow
grease. You will need to re-wax the spots with the FSR, anyway.
Others reported that SoftScrub worked well, but I didn't try it.
It was the non-skid (painted) that was most troublesome. Our non-skid only had about another year left in it, anyway, so we ended up just doing a fresh coat.