Alright kids I'm officially lost. My 94 SC300 GE NAT decided cyl #6 was going to stop firing. The motor has about 80k on it, original motor never been apart other than it had a thicker HG put on at like 45k miles. Here's what I've done...

1. Compression test (cold) showed 1-5 had 155-165psi and #6 was only 115psi

2. Did a leak down test and #6 sounded like the intake valve(s) were leaking into the intake plennum

3. I took the head off and it seems OK. I flipped it upside down and put some water in that cylinder and nothing leaked through, no bubbles etc.

Piston #6 looks fine too, no visible cracks or evidence of a leaking gasket. The valves on #6 had a lot of crusty buildup from not firing the last couple times the engine ran. I attached a couple pics below.

What else could cause the lower cylinder compression in #6? The only thing I can think is MAYBE a cracked piston ring? Not even sure that would cause a partial leak instead of a full on 0psi type leak. If anyone has any input I'd love to hear some ideas cause I'm just stumped!!