The inside of the block has a pin, with O-rings, and if they get messed up inside, it’ll leak out of the switch. The O-rings may be fine, just out of place, as with mine, or they could just be worn and need to be replaced. Its unlikely that the bore would be worn down, as the pin inside does not move, or shouldn’t move all that much.
Here’s a link to when I cleaned mine out and re-assembled it recently.
If you have new seals, you may just have it all in the wrong order, or they just haven’t seated well for some reason. The pin inside has a short side, which goes on the rear brake side, and the short side has 1 O-ring, then the divit or valley where the switch stays, and then it has a brass ring, then another, slightly larger O-ring.