1968 mercury 500 #4 cylinder not firing

[luckys pinstriping]

I have a 1968 mercury 500 and have noticed that #4 cycles run not firing. All cyclinders have good compression at 130-135 pounds, all plugs are also working with good spark. Any ideas what would chase this. Plug is clean as the day I put it in and seems a bit wet when I pull them. I would assume it is getting fuel not sure why it doesn’t fire

 

[racerone]

Look into crankcase compression issues.-------Reed valves.-----Lower crankshaft seal.

 

[luckys pinstriping]

Thank you, Racerone. Lower crank seal looks fairly easy to replace. How to i check the reeds?

Any thoughts on a bad exhaust manifold gasket or corroded exhaust baffle plate?

Thank you, Nick