Those fittings are unpressurised fluid supply. They seal with an 'O'ring. From memory the 'hex' area is cast into the cylinder and does not rotate or lock down the inlet tubes. If those seals have gone I would remove and overhaul the complete cylinder. IMO don't use any sealant to fix the leak, replace the aged seals. Here the parts from a brake shop would be about $30 for a complete kit.
Good - Fast - Cheap: Pick any two.
E23 735i; E30 318i; E32 735iL (X 2 - 1 White and 1 Light Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i