Lower Intake Manifold Leak

I have Olds Silhouette 1997 and I developed an oil leak which I diagnosed as coming from the horizontal space between lower intake manifold and the engine main housing. (the place where you put the RTV silicon gasket). A puddle of oil was collecting in the depression above the thermostat housing. I removed the upper manifold and found the lower intake manifold bolts so loose that I could almost remove them by hand. Got new bolts per the manual instructions and all the new gaskets. Cleaned meticulously all the mating surfaces, put new RTV sealant, torqued all the bolts to the manual specs. Just one day after putting everything together I am noticing the oil is collecting in the depression again!!!!! Is it possible that the lower intake manifold or the engine housing would have a hairline crack? Is there other possible explanation? Thanks for all suggestions.

It's much more likely that the oil is coming from the oil pump drive shaft. The top of the drive shaft is a silver cap that is held in place by a y-shaped bracket. The o-ring on the shaft was originally designed incorrectly and couldn't take the high heat and pressure, so it deteroriates. You can see the silver cap on the right in the below picture (picture taken when I was doing my heads...yours will look a little different.:) )
http://img169.exs.cx/img169/8436/40jt.th.jpg (http://img169.exs.cx/my.php?loc=img169&image=40jt.jpg)

To replace it, you can probably get away with popping off the throttle body which should give you enough room. If that doesn't, you'll have to go for the whole upper intake. Loosen the bold holding the cap down, take a pair of channel-lock pliers and pull straight up. The o-ring costs a buck or two at the dealer. Assembly is reverse of the removal.

Thank you! That sounds like a good possibility. The picture helped. It looks like your engine is slightly different. Your plug is kind of going vertically up-down, mine on is going horizontally. I do not have the diagrams in front of me to see if the plug is higher then the depression or not so that oil would flow down into it from the plug. If it is, it is good, at least I have something firm to go on...Will let you know.