All that "sludge" in the bottom of the pan is the thick old oil the previous driver put in the pan. Might have been used for all I know... You can stand the pannon end and it won't flow down the pan and my shop temp is about 50F...
The other thing is the last guy to assemble the engine must have used a full cartridge tube of silicone in place of gaskets... it was everywhere it shouldn't have been.
This is what happens when you "loan" out your engine.
From what I can tell it's a very heavy oil with a lot of motor honey-type additive. The guy who owned the engine ran 10w30.... this sure isn't that. Plus it has a ton of metal in it... bearing material, iron particles and such. Found one round mangled piece of a rod cap about 1/2" in diameter...