My 91 hatchback w/ the d15b1 has a leak. It's a gassy oilly leak coming from the valve cover. There is a 8-10 mm bolt that is loose where it coming out. If I tighten the bolt down- problem solved? Can anyone help, please.

 

If you don't know how or don't want to replace valve cover gaskets, tighten loose bolts and see what happens. If the bolts are bottomed out or something, then you don't want force them.