[chap52]

Ron, I think you may be overthinking this problem. If #7 is not holding air pressure there is a leak. Valve or leak over from the head gasket by an adjoining cylinder would seem to be the probable cause. Why not pull the intake and get a look at the condition of the valves, springs, clips and lifters.
If all looks right it's time to pull the head and look for a leak. For the cost of a couple of gaskets you will eliminate a lot lost sleep laying in bed and diagnosing the problem over and over. This I am sure is a common issue with most folks on this forum.
There have been times when my wife from across the breakfast table will notice a blank look on my face and say something like, "Are you working on the truck?". I figure my "thinking" for each adventure exceeds the actual hands on time by at least ten to one.
I also suggest as has been mentioned on this site by others that you rub down your gaskets with a very light coat of grease before re-assembly. It makes it easier to remove them in the future if you need to and saves on cleaning off an old gasket.
Don't get discouraged. Remember it's a "Hobby".
Your sharing the experience with the right group of understanding folks.
Keep us posted and enjoy the adventure.