It seems like on every gun that I have done I always have to scrape finish from the inlets to get everything to fit back together. On the one I just completed, I thought I would try something to hopefully make reassembly easier.
After every coat of finish I took a Q-tip (it was actually a medical type with a wood stem and tight weaving of the cotton) and wiped around the inlets. I just put it together and did not have to scrape at all. All parts went back in just like they ought to. Must have been my lucky day.