My 400 had only been driven a couple hundred miles in the previous 2 years before I bought it. Both 7 and 8 read low on leak down, the other six were right where they were supposed to be. Mechanic said to go out and run it 500-1000 miles, as long as i didn't see any overheating or oil loss and test it again. Two weeks and 600 miles later, all 8 were in the zone. He said he had seen it before with motors that sat around... me, I just felt lucky.