You may or may not have a leak here
I have a 1993 Corvette 40th Anniversary with 27,000 miles on the odometer. I have noticed a brake fluid puddle and a little fluid weeping between the master cylinder where it connects to the booster. I filled the reservoir with DOT 4 fluid, but the puddling continues. Is the seal between the booster and the master cylinder leaking or is there another problem that I am not aware of? Do you think changing the seal between the booster and master cylinder will solve the leaking?
The seal between the booster and the master cylinder may well be the problem, but I would diagnose the situation carefully before removing the master cylinder and booster. Is there any possibility that you dribbled a little fluid around that seal when you filled the master cylinder? Has anybody else serviced the car lately? It is possible that the stuff is just dripping down from an overfill or spill.
Next I would start the car and have someone step on the brake while you watch from under the hood to see if you can spot any spurting or increased weeping of fluid. And then I would check all of the hydraulic connections to the master cylinder to see if any of them are leaking too. Fluid has a way of running down things and going where you least expect it due to capillary action. Finally, I would check once again to see if the fluid in the reservoir has dropped at all after depressing the brakes a number of times.
If you do find a leak, I would remove the master cylinder and rebuild it. And I would check the rest of the brake hydraulic system as well, because if the master cylinder is leaking, the wheel cylinders and connections may be leaking too. The rubber in these components is perishable and does need to be renewed periodically. Better to be safe than sorry with such a nice performance car as the one you have.