115 is low unless you're running one hell of a race cam......it should be more like the 170 that Bomvida notes.

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Like you likely have a blown head gasket or a cracked head, especially with the wet pistons, dry plugs, and air escaping into cylinder 4 during the leak-down test. The 115 psi compression across all cylinders is a bit low but not immediately concerning if it's even. Still, I recommend tearing down the head to inspect the gasket and check for cracks.

How old is the engine build?  I am in the process of disassembly on my 1380 engine and my compression was reading 170 PSI across all cylinder however my engine only has about 5,000 miles on it

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Since all cylinders show consistent 115 psi, it’s likely acceptable, especially for a 1380 cc Cooper with flat-top pistons. However, since air escapes from cylinder 4 during a leak-down test, it strongly indicates a blown head gasket or a cracked head. Try to pull the head to inspect the gasket and check for cracks, especially around cylinder 4. The even compression suggests the block and pistons are likely fine Flicking Soccer.

Hello, I have a 1968 Cooper with a 1380 cc motor. Has a lot of goodies including a large valve ported 12g940 head. I recently had a loss of power and miss fire at high RPMs. After checking all usual tests like fuel electrical etc, I scoped the cylinders and saw wet pistons & dry plugs. I also noticed a fine mist in the cylinder 4. Any way after doing a leak down test on 3;all the air was coming out of cylinder 4. So obviously I have a blown head gasket or possibly cracked head. My concern now is that when doing a compression test all cylinder are pumping 115lbs. Should I be concerned ? Seems low. Piston are omega flat top. Should I tear down the block or as long as there even leave it alone . Thoughts?