While adjusting my timing last night I noticed a small but significant leak of coolant squirting out of where the intake manifold joins the engine.

The leak is just above the and to the right of the distributor when you're standing on the driver's side (left in the US) of the car. It looks like to me that the gasket between the fuel injection manifold (forgive me if I'm calling it the wrong thing) and the block has failed at that point. I also got a pretty good puff of white smoke from the exhaust when I revved it right before I noticed this leak. I shut down immediately; the leak continued for some time while I wiped around the area to remove some grease that had built up in the area to give myself a clearer view of the leak. As the engine cooled, the leak slowed and finally stopped. All the bolts in the area are tight.

My question is: does this sound like a gasket to you or could I have cracked something? In the process of adjusting my timing I have begun to notice a distinct clattering if I gun the engine quickly from idle, and I also noticed it on the road during a test drive. Under low, gentle acceleration the clatter is not noticeable, but if I get my foot into it (as I love to do) the clatter is quite loud.

Thanks in advance for your answers, folks...