The home I'm buying, which is about 10 years old, has a cream-colored vinyl siding. One side of the chimney chase is stained badly. The staining is worst closest to the top of the chase and less severe when it is farther from the chase cover. I thought the staining was rust from a cheap (builder's grade) galvanized metal chase cover which shows some rust. I had a roofer come by to look at the problem, thinking I would just have him replace the chase cover. I figured I could remove the rust from the vinyl siding. But the builder says the problem is NOT rust. The staining is from the home heating oil that is used to fuel the oil burner. I do not know how to remove the stains. He was not able to suggest any cleaner that he knows of. On-line research hasn't yielded any useful suggestions. If you have had experience with this kind of thing, I'd be most grateful for your advice!