1990 300CE fuel draining into intake, what would cause this?

[ROLLGUY]

I took my car (1990 300CE) to get smog tested, and it failed. They said it was running rich, and gave me a list of parts to replace (all rubber hoses on the engine, injector seals, breather hoses etc). I did all that including an oil change, and when I started draining the oil, I had to quickly put another pan in place before the first one filled up. I got about three gallons of oil (and I assume gasoline) out of the sump. When pulling the throttle body to replace the gasket, I noticed a puddle of gas in the intake manifold below the throttle body. I can only assume gas is leaking into the intake system somehow when it is running, and after the engine is turned off. What would cause this to happen? I am not as familiar with gassers as much as I am with Diesels, so please take it easy on me LOL! Thanks in advance, Rich