Weatherhead brake proportioning valve

Has any one rebuilt a Weatherhead 3549947 proportioning valve . My problem in the small piston between the two sides of the valve will not come out . The info I have tells you to tap the valve on the work bench or put air behind it from the rear brake side and pot it out . I am not having any luck doing ether , any help is welcome . I am soaking the valve in alcohol now to try get any old brake gunk loosened up . Waco Demon