Oil in cylinder no. three

It could be the crack has made its way down the spark plug threads. It may just be it looks like oil leakage because cylinder gases are leaking past the spark plug. A diagnosis from a shop you trust would be a good idea.
I’m guessing a replacement head is probably expensive there, so it’s probably worth paying a shop to do some basic testing so you don’t replace more than necessary.

That sounds good, the only thing I would put off is taking the manifolds off.
The rear stud on the exhaust manifold is bad for breaking off, so unless you need to remove them its probably not worth it.
You should be able to inspect and remove the valves with the head off and the valve cover off.

TERRY wrote: Yes, I strongly agree, don't mess with the manifolds unless absolutely necessary. Been there, snapped rear stud, broke off "easy out". What a PITA

X2!!!

Yep, saw some other post where someone was about to remove the manifolds to adjust the valves. Not a good idea.

  I prefer steel nuts installed with anti-seize instead of brass or stainless steel and have had no problem removing them.   After working on jet engine turbines section that used anti-seize on the fasteners made a believer of me.

 I should have said that I lived most of my 77 years in the in the Ohio valley about 40 miles south of Pittsburgh PA, the rust belt of the nation with all the steel mills and power plants in that area.

Oldpappy wrote: When I encounter a frozen nut, that won't free with penetrating oil or heat, before putting enough force on it to break anything I will split the nut to get it off, especially on small studs like those used for the exhaust manifold. If there is room for a nut splitter I use that, if not I use something else. I have used sharp chisels, and Dremel cut off wheels to get nuts off. The rear exhaust stud is difficult to get to, but removing the fender helps and is easier than drilling out a broken stud.