Power brake problem

My 66 Barracuda w/ an original Midland-Ross power brake booster and single master cylinder doesn't seem to be working properly. With the engine off I get some resistance on the pedal. With the engine running the pedal goes to the floor. With the engine running I've seen smoke coming from the bottom of the brake booster. I can't tell exactly where it's coming from but that is the general location. I also noticed a lack of fluid in the MC reservoir. I checked under the car as well as I could but didn't find any evidence of brake fluid leaking.

1) Is this a power brake booster issue or should I be looking somewhere else?

2) If this is a power brake booster issue should I have it rebuilt or go for a replacement?