Anything and everything Spitfire.

Please help!

My son and I are trying to refill the tandem brakes after a re-fit. We can fill the rear brakes ok, but no fluid goes into the front circuit (connected to S, secondary as seems normal if unexpected). Re-assembling the master cylinder, there just seems one tiny hole infront of the piston seal which could fill the front circuit (another hole to the side, which would be behind the seal, and the hole with the peg which stops the back piston moving forward).
Have we put the master cylinder back together correctly?
How does the front brake circuit get its fluid?
Could the problem lie in the pdwa (no fluid seems to get there)?

Thank you for any help!

A confused
Peter & Paul.