Hi Alan

I remember Girling well, i used to buy the wheel cylinder repair kits :)

Think Girling brake fluid was probably the main brand back then so manufacturers would recommend it

The brake master cylinder will have modern materials for the seals compatible with DOT4, its probably had wheel cylinders / calipers down the years so they will probably be a more up to date seal material as well

Just fit and flush through with DOT 4. I tend to use brake fluid from TPS as its very clear, some of the factors fluid is dark before you start, boiling point is probably OK but does not look that good

I been a self employed garage owner since 1977 :)

Peter