Finish Sprayer Gun Problem

I have this 20-25 yr old Craftsman finish sprayer.... ting-equipment-Parts/Model-919156350/0247/0733300/00013184/00001?blt&p rst=&shdMod .... that is "spitting" or skipping, as it sprays, leaving small gaps in my application, as I spray. I'm having to make double passes, in order to co mpletely cover the surface area and, in some cases, the double pass results in drips/runs. It started this about 2-3 months ago and I don't know what is causing this. It's been a long time since I've completely disassembl ed the gun and cleaned it.... Possibly trash in the inside?
I'm spraying lacquer. I initially thought water in the tank may be the, or part of the, problem, but no. I've always liked this sprayer and it had been adjusted to my spraying style/technique/settings.
What might be the cause and might this sort of problem be easily fixable? It may be time to spring for a new sprayer.
Thanks. Sonny
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