This thread has a method that worked great for me...
https://www2.mgcars.org.uk/cgi-bin/gen5?r...101901471513138
Here's the text from theat thread:
Posted 23 October 2000 at 06:15:25 UK time
Patrick Long, Illinois, USA,
plong@patents-tm.com
Have done the brake servo overhaul, not hard but not a snap either (no special tools involved. The AP Lockheed brake servo repair (Moss) comes with instructions (somewhat).
There are two tricks: One is to separate/put together the two halves of the servo housing (they twist off). The second is getting to the nuts on the inside of the brake pedal box that hold the servo to the pedal box
After taking off the MBC from the servo, take off the lid of the brake pedal box to access the top two nuts holding the servo to the box. Then go through the brake/clutch pedal opening in the cockpit to get to the lower 2 nuts holding the servo to the box. Trick using the 1/4 soket wrench set, use the socket, then a unversal connector, then a 2 foot long extension rod connected to the wrench. This will give you ther manuarability to get to those lower nuts.
Once the servo is off the pedal box, put several nuts (5/16 SAE Fine) on the two servo bolts that hold the MBC to servo. Tighten the nuts so all of thier flats line up. Then put the nuts into a bench vice to secure the servo (This avoids damage to the threads of the servo bolts.
Now put nuts on the four bolts (that are in a 2,4, 8 and 10 o'clock positions)which hold the servo to the pedal box. Place a ring spanner on one set of nuts/bolt (2 o'clock) so it rest down against a lower set of nuts/bolt(4 o'clock). Place a spanner on the set of nuts/bolt (8 o'clock) so the spanner rests up against the upper set of nuts/bolt (10 O'clock). Use the two wrenches to the twist the back end of the servo off to acccess the inside of the servo. Be careful servo has a big spring in it.