i really don't know how long the sludgy gunk has been building up in there. i do know that the oil i drained about 75 miles ago(when i 1st noticed the oil level was too high) is nowhere near as brown-chocolatey colored as the oil i most recently drained. don't really know if that means anything though.
i removed the intake manifold yesterday. holy sheet! where did this crap come from? there was about 2 tablespoons of gritty black sludge along the left side edges under the manifold. it reminded me of the stuff that i find when i clean my gutters. the presense of this gunk is not typical of 'just' a bad gasket is it?
i am thinking that there is no reason for me to tear the 3.1 motor down any further. i think i'll need to check out the integrity of the 3.4 motor that i got and go ahead with the swap if it checks out.
B-12 Chemtool will rip right through that sludge. I'd also run some kerosene or 0W oil to flush...again, IF you decide to salvage the engine.