"There is a small indent in the booster body where the MC bolts up to allow any fluid to drain, but clearly it isn't big enough so I've cut another groove into the MC mounting face so I'll see any leakage early on hopefully."
Some car and Motorcycle master cylinder ( hydr clutch and brake ) have weep holes.
Some power brake boosters have a bleed groove out the MV mounting face.
IF a leak develops where the push rod enters, AND there is no feature to direct it safely ( ≈ fail safe) , the errant fluid WILL go into the interior of the car or the brake booster.
The rubber in brake boosters does NOT like brake fluid, and vice versa.
A manufacturer who omits a weep hole in any component that attempts to seal liquid inside is either a crook or dope in my opinion.
“It depends on what the meaning of the word ‘is’ is.”
IF a leak develops where the push rod enters, AND there is no feature to direct it safely ( ≈ fail safe) , the errant fluid WILL go into the interior of the car or the brake booster.
Since you have the part, look for the weep hole. The photo did not have one and the OEM master cylinder does not have the groove.
Some other units for cars do.
You will know there is a leak because you will run out of brake fluid and should get a low fluid warning.
Channeling it is the worst option for safety. You won't easily notice the leak as you would a carpet stain. You would run out of fluid before the booster failed.
