It took forever to figure out what the problem was with the boom. I installed a new shiny Mosmatic 90 degree swivel and it would still leak. Took off the swivel and it looks like a good bit of the threads are semi-stripped. So I really tightened the swivel down and the leak went away. (This was the first time for that problem, I guess the car wash gods are eating away at the boom slowly and the booms life is coming to an end.) Since I tightened the swivel more it made the swivel too high so you could not install the high pressure hose (because of the hp fitting). So I had to make some extra room with my grinder.
While I was repairing the bay I decided to replace all the hoses and fittings. I used the black hose (6 foot hp hose) in the boom, then a brass coupler, then a 4 inch piece of stainless steel piping (to prevent the boom from rubbing a hole in the hp hose), then a brass 90. After I install that setup I added a 1 foot hp hose (swivel saver), next a swivel and then a 8 foot hose. You could then do a swivel then the gun, but I left out that swivel. I am not really sure you could tell the difference.
This time I purchased these fancy Mosmatic in-line swivels. They are shinny and look better for now.
Maybe someone could send in your bay setup and I could post some pictures?