Water on spark plug

I have a 78, crusader 270 that I had a loss of power on and returned on one motor. After return I fired up the motor with issue and it would run and idle fine most of the time but did stumble at times and needed to give a bit of throttle then would inlet fine for a bit and stumble again, it also had a noticeable ticking sound. Check oil and it was milky. So I pulled plugs to check compression.Plug from #5 had water on it. It was raining lightly at the time so I could have gotten the water dripping off the manifold but I don’t think so. #’s 7 and 8 were fouled as well, but we’re fine at last plug change this past spring. I expected to have low compression on #5 but it was fine. All were 120-126, except for #8 which was 95. On a recheck of 8 it was 80 ish. and on another recheck 70. Checked #8 with a bit of oil in cylinder and it was 85.

#8 plug also had a fairly large piece of metallic contaminant In it and #5 had a small piece contaminant but could not confirm if it was metallic or not.

I would say that 8 being down is blown head gasket. But what would cause the water on the 5 plug but the compression still good?

Thanks for any input.

Depending on where the head gasket blows it will not always cause low compression. I had both HGs blow with normal comp test results but water getting into 2 cyls. Upon disassembly you could see the HGs blown right next to water passages...

with water in the oil and over 40 years of service, I'd say it's time...

could also be the risers/elbows have rotted out allowing water be into the exhaust...

I ordered needed to replace head gaskets as well as elbow to manifold gaskets. looking at the Sierra application chart I picked the 3 hole gasket. After pulling the manifolds off and taking elbows off it turns my gaskets are the one hole version. After a double check the application chart indicates the 3 hole version, but a few pages further listed under a picture Of the elbow it calls out the one hole version. I would assume the 3 hole would allow more water flow/less restricted flow. What are the pro/cons of using the 3 hole? Would it be best to order the one hole version?

Also the elbows do not appear plugged or corridor through anywhere.

Thanks

specifics depend upon the cooling configuration of the engine...

typically, you want the one-hole gaskets where the raw water flows - their use is to ensure the water passages are (mostly) full to maximize heat removal from the cast iron. the three holes gaskets are typically used where the coolant flows.

and they are both orientation specific - install them incorrectly and the engine wont cool...