There are no gaskets in the brakes. And what's more, I don't think you can "fix the return".
If pumping the pedal brings it up to where you can apply the brakes, you need to try adjusting the rear brakes. The front brakes are disc type and adjust themselves. If you don't have a manual, you will really need one in order to take care of your new baby. Some folks like the Haynes manual. I prefer the factory reprint one from Robert Bentley. Either will be a good start. You may also need to find someone who has specific experience with these cars. Try to find a club in your area. Either an MG club or a British Car Club of some sort will provide you with references, I'm sure. You will meet some nice folks as well, who will be glad to help you familiarize yourself with the ways of MGness. But, get some reading material right away. The Moss catalog and others have a section full of books. They are the most valuable tool you can purchase. Go for it. And, congratulations. It's great to hear your enthusiasm.
Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon