Hi Bobby,
I believe Bob Spidell hit the points needed to rebuild the Girling booster. Due to a broken air valve, I was unable to rebuild and acquired a Lockheed booster. When finally finding the parts at British Car Specialists, I quickly rebuilt the Girling and have the Lockheed sitting on the shelf ever since.
I found the Lockheed to provide less assist and was ready to eliminate the booster and install a pre-BJ8 MC (as in a BT7). To extend on Bob's Girling-rebuild comments, if the leather seal is destroyed, you can replace the seal, however, it will require some trimming as the supplied unit has, historically, been too large and will drag on the sides of the vacuum chamber if not trimmed. This is a touchy area to address as a fit that is too tight will jam the piston and one that is too loose will diminish or loose the assist from the Vacuum/Atmosphere differential. Last, replacement spray-on lubricant was easily obtained and inexpensive before being designated a Hazardous Material. Today the same dry lubricant purchased in a spray can for $14 can be still obtained a much higher price.
Although I believe the Girling booster can be rebuilt by its owner, any of the conditions mentioned by Bob could make the attempt a waist of time. I also caution that many of the expert services have also made the attempt a waist of time as well so I, personally, would not be that positive on sending my unit before getting some guarantees.
The last alternative is to replace the booster with an aftermarket unit. I understand Tom’s Import Toys carries a PowerTune unit that is a remote booster from Australia (or is it China) that will provide equal or greater assist to the Girling. I was told by a Healey friend in Hawaii, who obtained his unit from a distributor in Australia, that there are multiple modes that will fit nicely with each provides a different level of boost, so choosing the correct unit will require guidance from Toms, or others with experience, to secure the model that will provide the level of brake assist (Girling-equivalent or better) you prefer. I would contact Tom’s to get further information, as I was told the cost of this unit is very reasonable when compared to having the Girling rebuilt and other replacements. I believe these units are sold under different names and some on the list may have some experience and will share.
Good luck,
Ray (64BJ8P1)