I have some Topre CC that just slid into the stem smoothly. There's no resistance, they feel easy to fall off and yet they stay put. But, I imagine that the more I put and take them out of the board, the more the plastic skin will rub off each other and it will come a time it will be super loose. It's inevitable, isn't it? Especially when it is an old clack.
When I had issue with the Bro set (MX) modifiers fitting into the keyboard, some members suggested putting a tape on the stem. I tried that and it worked. Can't you do that on the Topre cc, nubbs?