but I've had an
oil leak in my XB3 crate motor too. Mine was at the #5 cylinder location, but was pooling
oil on the lip on the bottom edge, topside of the valve cover. Turns out it's a crack in the cover, so fine you cannot see it - discovered when I yanked the cover and saw that the exh. rocker arm was rubbing on the cover. The inside of the cover (at the rocker location) was polished about 1/8" dia., and this had also caused the crack. Would weep
oil only when running, and had no discernable source. Cure, until new covers arrive, was to shove the cover upward as much as the bolts will allow, and tighten down there - pretty much stopped the problem. Like I said, not sure if your troubles are similar - but worth a check.
