Was in a large music shop Friday having a few dinks removed from my Bach Strad 72*. Talked with an individual (will keep his name confidential) that, though elderly, is a master repairman, has designed several trumpets including one of the most popular student horns, and holds several degrees in engineering. He has also worked for Olds, Bach, and others years ago. And he played with the big bands. That information provided to substantiate this comment was not from a Middle School student but someone with a great deal of experience with trumpets - especially instrument repair.
I asked about having my horn chemically cleaned. He responded that you don't want to do that. Said to just use a snake or such and give it a good cleaning. He then said that there was another shop nearby that pushed regular chemical cleaning and he gets business from many of their customers complaining of valve problems. (I know the tech at the other shop and asked what they used - he said something or another Green for the soak.)
So, does anyone think chemical cleaning could be harmful? Personally, I have never had a horn chem cleaned, but do my own cleaning with a snake. Have used one horn from the 60s and still no problems.