Replacing the gaskets makes sense. But the caps look identical to the ones that are already on the master. Wondering why the need to replace the caps too?
Because they’re just cheap plastic and the tabs seem to flex, which keeps them from putting enough pressure on the gaskets.
You can try just changing the seals and see if that works, but if it doesn’t I’d change the caps next.
I’m not sure what it is, the caps should be a non-wearing part but it seems like if you take them on and off a bunch (like if you’re changing a bunch of brake parts and bleeding them a few times) they just don’t put enough pressure on the gaskets anymore.
