Twin & Triplock crowns contain a spring/plunger assembly, which is what allows the crown cap to move (laterally) beyond the point where it contacts the tube. This is part of what makes the water-tight seal. In this case, as jmb suggested, you need a new crown, which should screw onto the stem. You will need to remove the caseback & (carefully/gently) press the stem release to release the stem to fit the new crown. As this is a common problem with aftermarket crowns, if you plan on keeping the watch, I would replace with a gen crown (check ebay) &, since you have to remove the caseback anyway, I would have the movement professionally overhauled, so you are not back here next week posting that the watch stopped right after having the crown fixed.