Engine oil or tranny oil?
It looks too dark to be fresh engine oil.
BTW, those chrome necks are almost impossible to seal. No they're not if you resurface them for about 2 seconds on a belt surface.If you really want to use it, you will need to machine it dead flat, and open up the T-stat receiving flange. Then you will need to stud the manifold, and the top of the stud needs to be fine thread. Studding a T-stat housing with fine thread studs? Really?Then you will need large,thick,hardened washers and grade 8 self-locking nuts. Do not use loc washers.Fit the washers as may be req'd.Do not overtighten.If you overtighten it, it will warp, and you are back to square one. Use exactly one good quality .030 to .040 gasket(I make my own from that blue stuff), and no sealers.Use a 7psi cap.n Again why?
That's what worked for me.