ohhhhhhh-ring!
 

OK, so I pulled the MC away from the booster. No sort of rubber ring to be found. A-Ha! You guys are the best. There are a couple of grooves on the M/C where it touches the front face of the booster, and then there's the cylinder itself that sticks into the booster. Which location does the o-ring go to? and, who knows what size ring I need? The haynes manual doesn't say, and the steaky site is down :mad: . I asked at Autozone, and of course their computer sez "we don't carry that seal..." If this is something I can buy @ a generic place that would be great, since this car is my daily driver. Thanks againg for all your help.

it fits over the protusion of the mastercylinder....measure that and you have the size you need from your hardware store. I don't have one I could measure right now.

Answer:
 

Attached pictures.

Our 83 had no seal ring of any kind when we took off the M/C, but the brakes worked fine, and were VERY powerful. What does that mean? :D ;)

We are putting one on when we reinstall it however...

booster vacuum seal ring: 1 5/8" ID, 1 7/8" OD
 

Just measured it FYI, those are the measurements for the booster vacuum seal ring. Needs to be 1/8" thick I think, best in some brake fluid resistant material. Now I just need to find the darn compass and cut one from the make your own gasket material... Thanks again guys.

It means you didn't look close enough......and the old O-ring was flat as a pancake....because that is what seals the Booster vacuum in.....you WOULD have a massive vacuum leak without it.

pick up a generic O-ring at the parts or hardware store .....many have those kits that will sell you a single O-ring from....

o-ring from napa, $0.75, stopping and shutting off, priceless
 

Picked up a 1 5/8" id rubber o-ring from napa, tightened it down and voila! Brake booster sucks the pedal down a little on start up, and the engine shuts off with key. Hurray. Nothing like successful pre-work repairs to start your Monday off right.:D