brake problems
 

If you ever find yourself having to fill your brake fluid alot and you don't have a leak, lots of supra are known for leaking from the back into the booster destroying your booster and not allowing to have power brake which is scary to drive without.

Not a common problem
 

This problem is NOT all that common, in Supras or any car. It can happen, but usually the fluid leaks out between the master cylinder and the booster. It can be seen, and signs of the corrosiveness of the fluid, on the booster. Then, You can just replace the master.

Also, I have seen fluid dripping out of the booster at the bottom. Then I would recommend a booster change, as a future failure is coming.

Boosters, as an automobile component, are actually one of the longest lasting things on a car. For a part that is used / moving parts, so often in a cars life, I am very suprised that more don't fail.

After more years in the business than I care to say, and having done (or assisted with) more brake jobs than Midas (just kidding), I have only replaced about 4-5 boosters.