My goodness, that's a tricky one... i think i found one:
I would double check with a bolt first. See if a 3/8-24 bolt starts into the fitting (that i think you're saying is on the 3/16 line), also check if a 5/16-24 nut goes onto the oil line (that I think you're saying is 1/8). If so, it seems like a 37° JIC fitting.
