3.1 Intake Gasket problem?

We have a 99 buick Century with the 3.1. Recently noticed gunk on under side of radiator cap, had a dealership flush the radiator. After 300 miles, took another look at the cap, looked horrible, same gunk. Took back to dealership, they reflushed and told us the engine my have a intake leak. How do I know if that's the problem? Engine has 103K on it, we have owned since 60k. Is slightly down on oil, but needs changed anyhow. Coolant kindof feels oily. What's my problems? Thanks Joe

If you are running Dex Cool in your cooling system this is normal. The dex cool will produce this brown gunk on the bottom of the radiator cap and inside the coolant reservoir tank. If you are not seeing water in the oil and the coolant level doe not drop then you really don't have an intake gasket problem.

Welcome to AF!

I would also suggest a new cap to insure no leakage, this can accelerate the contamination you see in the neck/cap.