I agree with Eagle that consistent fitting of the transmission in the WC American Classic Ball point design is problematic.
However, unlike the ballpoints, the WC American Classic rollerball does not have a transmission. The snap on cap has sort of a plastic o-ring which compress fits a slight groove on either end of the body. It seems to generate a different problem - sometimes fitting too loosely and sometime too snugly. I've not turned a whole bunch of them but have had success with the adjustment described in the instructions.