just a thought scott, i was wondering if, rather than take the plastic cart down to paper thin ,heat the metal mouth piece up to the point where it expands, maybe put it in boiling water, or heat it over a gas flame before you take the paint off, have the plastic cart machined down slightly but not as much as you did, then holding the hot metal with pliers, push it over the plastic.I guess if it was hot enough it would soften the plastic to make it easier to insert aswell,,,,just a though!!!