Oil pooling in '68 340 factory intake manifold....

This is the trick guys.
I had the same problem with mine, right on both sides of the crossover.
Pull the bolt, and give the threads a light shot of carb cleaner then blow it off with canned or compressed air. (No it won't bother the oil in the motor because it evaporates so fast)
Silicone the bolt threads and up under the bolt head where the head meets the bolt shaft and put her in.
I use a stainless steel toothbrush sized brush to take of any extra silicone from around the bolt head AFTER it dries.

Done deal.