[Jim Sims]

I believe the question mark on your figure is directed at the nut side of one of the case through bolts. This bolt is one of the structural elements of the engine; it resists crankshaft loads. It is an "acorn style nut" (Item 28 in the figure is one of these nuts) so it looks somewhat like a bolt head. Underneath the nut should be a beveled washer (item 27) and under the the bevel of the washer there should be a rubber o-ring (item 26). The washer and o-ring are required because the holes for these through bolts are also oil galleys and hence must be sealed. If there is oil coming from the nut it is either loose or the o-ring has failed. I'm not sure but to get to the head of the bolt on the other side (passenger side) to attempt to re-tighten you may have to remove some of the air conditioner system brackets (if equipped with A/C) and the sheet metal/plastic hot air ducting at the rear of the engine on the passenger side. Check the passenger side of the engine. If the bolt is tight then the o-ring is likely bad; I don't know what the risk is of loosening this nut and replacing the o-ring and then re-installing and re-tightening to the correct torque. There may be a risk of starting a leak in the sealant around the case seam or nose bearing if this bolt tension is relieved. Perhaps someone with more experience will comment. Cheers, Jim