318 oil leak

Get a timing cover gasket set. Is your harmonic balancer actually bad? Your timing chain set, plastic top gear or steel?
If your engine has been apart, sure that it has, its probably a steel set, is the chain loose or tight? Your already in there, do it.
Pay attention to the length of the bolts , the lower right of the timing cover , it's short and goes into the water jacket, make sure you get that one right, a longer bolt will crack your block. There are only three bolts to put thread sealant on, the one that I just mentioned and the two lower of of the four long top bolts. Get teflon thread sealant, you can use silicone, but I wouldn't.