What would cause oil to appear around one of the intake manifold bolts ? I have checked the bolt for tightness and it seems fine. If I clean it off, it reappears after a couple of days leaving a small puddle around that bolt.

Oil is just seeping up the threads. I had the same problem. Take out the bolt and put some kind sealant on it. I used some teflon pipe dope.

I had the same problem. I used Teflon tape
available at any hardware store for under a buck. Just wrap the threads of the bolt a couple of times then torque it back down. No leak!!!!!

The best stuff is permatex thread sealer with teflon. Comes in a bottle with brush in the cap. The other stuff suggested also will work.