when you buy a car look very closely at the contract you are signing. Usually you have 30 days to return it if not satisified. Some states also have lemon laws that mandates that the dealer must take it back under certain conditions. Check out your local states lemon laws.
the same thing can be said for any work that is done on it. Look at your contract, Is there a warranty? Most likely there is and I would take it right back to them. If they won't fix it ask for your money back or take them to small claims court if you must. Take pictures or a video for evidence, before getting your car fixed.
The 3800 is one of GMs best engines and should have minimal problems. Alot of people get 200,000-300,000 miles out of them.
If the dealer won't fix it. Use an engine cleaner on the engine and powerwash it off. Try to keep water away from the electronics. Refill engine with oil and notice where the leak is coming from. If no visible signs the engine must be burning the oil.
Maybe you could go to a higher weight motor oil. Like straight 20W instead of 10W-30. I don't know if this is a good idea with the 3800. Check out the other Oldsmobile forums since most Intrigues are 3.5L --a totally different engine.
I'm sure a good GM dealer will find that leak right away.