I have seen those deposits on the furnaces all the time and it's impossible to make the glass without the deposits. My impression is that there should not be anything coming off of the glass that would cause that on the gloryhole aside from migrant dust from the batching as you suggest. That would in my estimation be a lot of migrant dust. I don't get that on my gloryhole when I melt leads but I do have it on the furnaces.
Lead is also a drag because it doesn't leave any symptoms and I don't think it would cause headaches. As they say irt's a silent killer and all it does is to make you stupid- and I'm not trying to make a joke. I think your torch is one possibility, but only one. I'd still bring in a CO detector if you can get one. Lead shouldn't cause headaches,(again) I don't think.