Has anyone replaced seals in a ABS master cylinder? I've taken the outer piston assembly out but the inner one seems to be blocked by some sort of pin. Other master cylinders I've worked on have had screws going thru from the outside but there's nothing obvious that I can see other than a split pin in the bottom of the front fluid chamber well. Does this have to be drilled out? There's nothing to grab 'cause it's flush with the bottom of the chamber.