I'm scraping old wood siding that's been covered by vinyl for years. This is the first time I've scraped with a heat gun. It's very gooey and leaves a residue behind. It's sticky when hot, but dries hard and is firmly adhered to the wood. I'm not able to scrape it off, but I could probably sand it off. Is this common? Since it seems to be adhered so well, and since I presume it's just paint, is there any harm in just leaving it?