I recently purchased a 1997 Monte Carlo z34 with about 86000 miles on it. Less than 2 days after owning it. Had it taken to the dealer to have a head gasket job done. (Didn't need it but didn't want to spend 1600 on a oring, the real problem) Now its been about 3 months since the job was done. Didn't have any problems with it until the last few days. Started leaking oil on to the exhaust. between the firewall and the engine.
Having waded into the water with a spark plug job, I decided that it was most likely the valve covers leaking as I and that was simple enough. When I got the upper intake off, I could find no oil leaks from the valve covers..I found the wet oil under the valve body assembly (probably not what it's called) just above the manifold. Using a mirror I checked to see it it look like the gasket was coming out. Looked just like the front one did, and the front doesn't leak.

What I'm wondering is when I took the back cover off there seemed to be a lot more oil left in with the cams than in the front. Could I have a draining problem and pressure is building up in the valve body assembly and coming out. Oil shows no sign of having coolant in it and the oil I can wipe away above the exhaust is clean? Just how does the oil get back down into the crankcase? Just wondering cause its do to go back to the dealer for a check out to see if something they did has failed. (History of the car is unknown, but from the what I can tell maintenance wasn't high on previous owner's mind) Dealer said timing belt looked to be original.

Sorry about the long post.
thnx for any help.
I'm getting really quick at getting the upper intake off and on. down to 1/2 hour from my previous 4 hours. two of the 10 mm on the egr valve pipe gave me trouble had to recrute the wife's smaller hands.

 

On the block of the 3.4s there is an oil pump drive where the distributor would be if it wasnta coil pack ignition. It has an o ring seal that is prone to leaking. Have that checked out. I would take it back to the dealer and say it is leaking and it started after the job was done. Have them fix it or at least take a look at it.

If your timing belt is still original I would have it replaced NOW. Dont procrastinate. They only have a life of 80,000 miles and these engines are interference engines so if the belt breaks your engine is f***ed.

Sounds like you are becoming a pro at removing the UIM. I had mine off 3 times just to replace the spark plugs (problem with plug gap). I am down to about 15 minutes. The throttle body runner is the hardest to unbolt. Next time I have the intake off I think I will just pull the throttle body off the runner and take the runner out with the intake. Im 6'2" so my hands are giant and dont fit down in the space available to unbolt the runner.

 

Had the timing belt changed, the "leaking oring" changed along with the both banks of head gaskets. some plastic pulleys. and other gaskets that were removed in the process.

The new leak is something I've haven't found in this forum or elsewhere on the net. The leak isn't from the valve cover gasket, but the one below it. Looks to be the same material as the head gasket, but sits between the heads and the body holding the cam shafts. The front bank doesn't leak.

I originally thought it was a valve cover leaking, but during the change out I noticed that the rear bank had more left over oil pooling inside with the cam shafts. And the edge of the valve covers were dry on both banks. So changing valve covers didn't help and the car still leaks oil after about 5-10 minutes. Any longer and the oil starts dripping and actaully making it to the ground. The leak actually gets worse the longer it runs. I thought at first it might be a heat problem but letting the car sit as little as 5 minutes is enough that it doesn't leak when it is first started and it takes another 5-10 minutes for it to start to leak again. I wouldn't think a fully warmed up engine would cool down enough that I would have at least the smoke coming from the burnning oil as it dripped onto the exhaust manifold.

I'm wondering if I might have a plugged drain and the excess pressure from filling the cam section with oil is causing the leak.

I'll be finding out for myself Friday after work when I remove the UIM again and the valve cover and see if I can find these drain holes.