"As far as leaving waterborne product in your gun,
I have been told NOT to do so."
I heard the same advice, I just didn't listen and have experimented with various products in my gravity guns made for WB product. Most clear WB based finishes, with the exception of post catalyzed products, I haven't had any problem. If I had a gun without stainless passages and attachments or a typical bottom cup gun I wouldn't leave product in the gun. The reason it works, in a gravity gun is there is no exposure to outside air so the product can't cure just like in the original can. At least now you have a differing opinion to commonly given advice and possibly make up your own mind.
John