Could be serious; but, then again, maybe not
I've seen this before and sometimes it's caused by a serious problem, sometimes it's not so serious, but in both cases, what you most likely have going on here is corrosion beneath the paint that is causing the paint to flake off. Corrosion is a problem that needs to be tended to or it's only going to get worst and result in some kind of failure at some point. Corrosion to aluminum is what rust is to steel and iron; principally the same process, just different manifestations of oxidations. If it is just simple corrosion at the attachments, then, yes, it's like that a good wire-brushing, some anti-oxidant treatment and quality paint will cure the problem. If that is the case, I would recommend making sure the metal is perfectly clean, treat with a product known as Ospho, shoot some zinc chromate on it as a primer and then paint it.It could also be electrolysis between disimilar metals, i.e., the mast/boom are aluminum and the fittings are a different metal, i.e., stainless steel or even different alloys of the same base metal. This is a more serious problem than simple oxidation in that electrolysis eats away more rapidly at the lesser metal in the mix, i.e., aluminum is attacked by stainless. There is a natural galvanic process that takes place between dissimilar metals and this flaking of the paint only at specific points where different metals metal would be evidence of that. Electrolysis promotes rapid corrosion and electrolysis can seriously weaken and even destroy or cause to fail various types structures. In some cases, particularly with aluminum, you sometimes get what's referred to as "filligree" or bunches of tiny holes.Certainly, you have a corrosion problem and I would suspect you have some electrolysis figuring in there somewhere too. You could face some fairly pricey fixes for these problems.Now, your question was semi-general and I've given a semi-general opinion. What I would do is go ahead and carefully flake some of this loose paint off with say the tip of a pocket knife and see what's under it. Then, I would take a point object like an ice pick or a scratch-awl and kinda gently whang away in the areas where this problem is occurring. If the corrosion problem is bad, the point end of the pick or awl is going to penetrate. If that happens, you got problems...or you're gonna get some reduction in price so you can fix this. Another thought...if you have some chaffed wiring to your masthead lights, spreader lights, instruments, whatever inside the mast and you are getting some DC leak, this could be causing an electrolysis problem, too, and that would certainly show up where dissimilar metals meet. You might want to haul the boat and take a hard look at the shaft, cutless bearings, rudder posts, strut and prop, too, in order to inspect for corrosion. If you have a DC leak, it won't be just on your boom and mast that you are having a problem.Oh, and if the broker howls at you whanging gently away on the corrosion and objects, go find another boat.Hope this helps.