Are you certain the 'goo' isn't from a tranny cooler leak in the radiator? It wouldn't be the first time that happened. Import car water pump impellers have a curious habit of dissolving, melting or spinning loose on the shaft at times. In fact I just did a 929 today - the impeller spun loose, the car overheated and the hot water from the top hose torched a nice big split in the top radiator tank. Aren't plastics wonderful in realistic applications?
Anyway, was the car running normally or was it mis-firing, white smoke in the exhaust, smell of anti-freeze burning, etc.?