I think my 727 is fried. Now I'm at a crossroads...

An overheated or failing converter will cause puking of fluid out of the vent. Plugged oil cooler or kinked lines are the usual culprits. A sticking converter control valve in the valve body is always on my list. I've run across a few that didn't have the baffle plate installed over the inside of the vent hole too. Blowing fluid out of the vent commonly takes place sitting in a traffic jam in drive, or when pulling up a long grade at low speeds.
Failed front seals and cracked converters leak all of the time, and never heal up, so your problem isn't likely either of those. Too much fluid, contaminated fluid, or poor quality fluid should always be looked into. If I were you I'd repair the kinked cooler line, blow out the fluid cooler/heater in the bottom of the radiator first. If the converter has a plug I'd drain it and the pan and refill with top quality ATF+4. If the converter doesn't have a drain plug I'd drill and tap it for a 1/8 pipe plug. It's a drippy job but it doesn't take long and all the metal chips you make will be flushed out while you are doing the job. Worst case you have a worn out pump housing, reaction shaft, and/or pump rotors. If the pump isn't good enough to keep up at idle speed the converter will drain back some which raises the fluid level in the pan high enough to get whipped up by the rotating parts once you get moving again. Foamy fluid will make it slip and leak from the vent. Happy hunting!

Steve