Our vacuum generator started leaking air a couple days ago inside it's little black box (located on passenger side of generator enclosure). It would drain the main air tanks in about 30 minutes. I talked to Bob at Foretravel and he said parts are no longer available for this, but they have a solution. They are sending me parts for about $265.
The quick fix for the air leak was to fold the air supply line in half and tape it so it won't unfold. That is working. He said I won't need that air line because the new part is electric.
When I put my finger on the vacuum port, the pump shuts off immediately. Also, when I pinch off the vacuum tube into this can (see photo), pump shuts off, but when I pinch the tube "out", it keeps running. The can is needed to support the stock vacuum generator. Without the can, the generator goes belly up very quickly.
UPDATE: Finally got this project finished. FOT no longer has a source for the vacuum reservoir; at least not now. The factory quit making them in about 2006. A neighbor suggested filling mine with water to see where it leaked. Found the leak and he gave me a marine epoxy sealant to fix it. Now the doors in the dash hvac work again and no air leaks!
As Pierce said, most any vacuum generator will work. The one from FOT for $260ish is a Ford part available new on eBay for about $50.00.
Old and New Vacuum Generator
Vacuum Generator in and Reservoir repaired
Part number. E3 HT-2A451-BA by Dick 2003 U320 40'
Here is how I found my problem: Let the pump run with the key on, open the compartment door and locate the pump by the noise it is making. Find the suction line at the pump and using a small ViceGrip or hemostats , pinch off the vacuum line a couple of inches from the pump until the pump stops. Then work your way until you come to a connection where the line separates and goes off in different directions. Clamp one or the other lines until the pump stops. Just keep working further and further away from the pump until you find the problem.
I pulled the wall off the front of the heater/dash AC and checked all the vacuum actuators until I finally found the leak in the AC/heater dash control unit right in front of the driver's seat. Took about an hour to figure it out.
Using this method, you don't have to pull any lines off, just clamp them so it's fast and EZ.
If the vacuum pump is anything like the pump in the nose of a GV, then any reasonable 12 volt vacuum pump will do the trick. In a GV, the Ford air conditioning dash panel has a problem with the sliding lever. On many, if it is all the way to the left, it starts a vacuum leak and will cause the vacuum pump to cycle repeatedly causing it to wear out before it's time. Putting a stop 1/4" before the end fixes the problem. Pierce 1993 U300 36'