No no no no. You have a Zero loss brake valve. This is NOT the same as an M Valve which you can use as a brake valve or a SA retract valve. The M Valve is half the size.
Almost certainly nothing wrong with the retracts, SA system retracts have always been less hassle than two way air up down systems where there cannot be a leak. This is not a leaking problem, its a wrong valve problem.
What sort of valve do you have on the brakes? Same type or the single smaller, M Valve? If the same type you need a new valve. If you happen to have a single on brakes (not one that says Brake valve on the side like this one) you can swap.
The internals of the zero loss brake valve are completely different.