It looks more like a condition called 'acid bleed'.... where the flux from soldering the bow guards and wires crept out from under the parts after the lacquer was applied. The only way to find out for sure is to buff off the remaining lacquer in the area and see if the red goes away. If the red goes away, and there are no perforations in the brass, just spritz on some lacquer or clear-coat out of a spray can. If there are holes in the brass, you need to have the horn repaired by a professional.
BTW... what brand of horn is this?
Dan Schultz
"The Village Tinker" http://www.thevillagetinker.com" target="_blank
Current 'stable'... Rudolf Meinl 5/4, Marzan (by Willson) euph, King 2341, Alphorn, and other strange stuff.
If you have the slightest suspicion, that an instrument is infested with red rot (loss of the zinc component of the brass alloy), then stay away from buying it, if you are out for a workhorse instrument.
I have some instruments suffering from red rot, at least one that is. But then I am collecting for museal documentation purposes.
Some brands of certain periods are more prone to suffer from red rot. There are two quite effective methods to avoid red rot: changing the alloy to red brass or to nickel silver.
Another vote for acid bleed. Older Edwards / Getzen trombone bells are notorious for the problem, but it occurs on many brands instruments. Even seen it on a Mirafone or two.
I often see pink/redish staining like that after a chem clean on my own horn on spots where lacquer has worn off as well as flux bleed on a couple slides. It doesn't necessarily mean it's a bum horn... I hope! I mean, mine's a Nirschl.. I hope not.
These pictures were from an eBay listing for a 1972 Mirafone 184 CC.
After consulting with Lee Stofer, who went with the acid bleed theory, I bought it.
The price was good enough that, even if it needs a small patch, I'll be ahead. The rest of the horn (with factory fifth valve and original case and mpc) is absolutely cherry--no other dents, scratches, anything. It should arrive late next week. Wish me luck.