Well imho you have the right rifle then lol . Oly has a spotty reputation both on customer service and on the actual quality of parts used . Not to throw rocks at your rifle , but you paid little , and got little . Most of the folk i know that go the " pistol ctg" AR build their own , and it looks like you will before its over . One suggestion ill make is that as a rule " pistol powders " are dirtier than rifle powders , so possibly you need to look at the powder your ammo is loaded with and choose a cleaner burning brand , or go to reloads with a " clean " powder for a " cheap " fix . Other than that ill speculate that you are a victim of " tolerance stack " where every part falls within tolerances, but the way the tolerances work with each other ( one being on the minus side and another on the plus side ) you get a rifle that is sensitive to fouling . You mentioned your dad was a toolmaker so query him on the concept as needed lol . If you want a quick fix ( and since you have apparently fixed the " lower " issues i would suggest that you " gut " the upper and replace the entire BCG with one of known quality and dementions ( yea just what you wanted to hear lol ) . While your at that go ahead and " mic out " the upper to make sure its both in the middle of " tolerance " and true ( you can peer thro it and it looks fine to the eye , but in fact it can be cut " offset " where the bolt has to cam into lock creating a problem, a proper reciever is cut square along the axis and for the record a receiver that out of spec would be uncommon but not unheard of ) . In Oly's defense they are getting much better than they used to be , but that brand is still not on my short list of ars ill buy ( its gotta be a heck of a deal for me to get one , and its not going to be a keeper if i do ) . I suggest you look at it this way , You have a lower setup to take glock mags , and the upper is the non registered part(s), its a great starting point .
It was fun working on it. I use "SKILLS" I have not used in years.