The Girling OEM Brake Master cylinder Reservoir seals are available on Ebay.
I found them while searching the original Girling Lucas Number from the original seal itself. 2274660098.
I previously bought both the aforementioned Jag153 and JLM11828 and they ABSOLUTETLY will not allow the reservoir to seat fully in the Master cylinder. Its not like I did not try several times ...I bought three sets as I had two M/c I wanted to do. You can get the seals into the M/C and then wrestle with the reservoir or even a slow press with a c-clamp to get the reservoir into the M/C . yes I lubed them up plenty...no joy.
SO I get OEM from ebay ..Girling is molded into the top of the seal and the 2274660098 number is on the bottom. PERFECT FIT. I talked to the vendor for the oem seals and he has about 50.
IF someone has been successful with the JLM11828 or the JAG153.
PLEASE let me know your process for this.
They are listed as fitting the 88-89 M/Cylinder That is why I bought them.