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These engines are strange like that. The 360 I ran before building my current motor is a great example. Number 8 cylinder wall was so egg shaped that I could see the head past the rings from the bottom (bad plenum caused stuck rings, which caused excessive wear). The only reason I realized how bad it was was because the Piston slapping sounded like a bad rod bearing. Even with number 8 doing nothing, it still ran smooth and threw no codes. I just noticed it was a little down on power before the noise started, which I just blamed on several very hard years on the engine.

Point is, listen to these guys in here. Try the leak down test again and if you get the same results plan on at least pulling the head and getting it checked out. Be ready to find some real carnage inside and possibly drop another moto in or rebuild that one.
Plan for the worst, hope for the best. Good luck.

 

You can have a dead cylinder, or two dead cylinders and an engine that seemingly runs smooth. An eight cylinder engine is just a four cylinder engine with four additional cylinders that help it along. The feeling of a miss is totally subjective and a whole lot of other stuff comes into play on whether or not a dead cylinder is going to act like a passive missing cylinder or a something that is going to mess up the whole party. If #8 occasionally fires, you'll notice it. Your #8 cylinder provides 1/8th of your power and you'll lose a little more because the other 7 are needing to drive #8 up and down. But you still have well over 180 HP if the other 7 are cooperating and it's likely that you wouldn't know the difference unless you tried to pull a trailer or climb a steep hill. A dead cylinder, depending on a lot of stuff, may or may not cause a noticeable or obnoxious running issue. If you only drive short distances and don't require all of your power, the truck could potentially run for years getting you where you want to go every day. My 1978 Camaro with a 350V8 only had 170hp when it was new. However, the engine is most likely not going to pass an emissions test and fuel economy is going to be less. Other stuff may or may not happen.

 

I had this problem a year or so ago. My #6 exhaust valve burnt. The truck ran fine, with just a little reduction in fuel economy. It idled rough, because of the misfire. Leakdown test confirmed the valve with a steady hiss in the tailpipe. Trust test results. They seldom lie.