Stalls when I brake hard. Last year I buttered up the brake booster seam with RTV the problem seamed to go away. Now the problem is back. Is it the seam or is the booster now toast? Is there a test to be sure before I start throwing parts at this beast?

Will it die if you are just sitting still and apply the brakes?

You could verify the leaking (or NOT leaking) booster by disconnecting the vacuum hose from it, plug the hose, and see if the problem disappears. Of course you would have no brake boost during this test so you would want to be very careful if you drive it, and be prepared to have to really stand on the pedal to stop.

You might check the engine wire harness, particularly at the AMM connection on the driver's side fenderwell. I had similar trouble earlier this fall, on my '85 245 with a non-turbo B-230, AW 71 tranny, which would stall whenever shifted into reverse. I found the connectors in the harness AMM plug and the AMM terminals dusted with a white precipitate from a recent engine wash with a power wand. Cleaned both sides of the connection with a toothbrush and contact cleaner. End of problem. Apparently the leg of the wiring harness which serves the AMM would swing enough with the torque of shifting into reverse (or a right turn at slow RPM) that an already iffy connection was compromised. Braking, I assume, could cause a similar pull on the harness leg.

Sounds like a bad vacume leak at the seal on the booster,but it seems if this were the case you would have a hard pedal and rough running engine all the time.