Vertical mani where it meets the head has black crud.
Looks like an oil leak. Maybe dripping down from a leaky valve cover?
Also I do know for certain that the exhaust cover on the horizontal head is leaking some oil.
Does Chris sell gaskets? I couldnt find any on the site.
Get the "rubber" coated OEM valve cover gaskets, they last forever.
Mine are like thin metal ones with a grooved pattern embossed on them.
So my guess about the sludge around the manifold is from oil collecting is likely correct?
Those are the good gaskets, if they have a thin black rubbery coating.
Clean off whatever sludge is bothering you.
Clean the gaskets with 'carb cleaner' , same for the mating surfaces.
Confirm that the mating surfaces don't have any burrs or dings.
Reinstall.
See if it returns.
From what I remember they were not sealed in rubber. Unless it's so thin that I didn't notice.