Just wondering if anyone else is experiencing this. I have a silver x-long manual and a white one. I have a variety of carts purchased at different times. On the silver one, any and all carts fit and work fine. But on the white one, some do but a lot don't. They just won't screw down far enough. And I have tried using a bit more force but when they stop, they stop and they just won't go down any further. Have the same prob with one of the manual passthru's. Upon looking at the connection end of the carts closely, I can see that there are some differences - small ones but they are there - and this seems to be the problem. Do you think if I just took a file and filed the end off a bit it would hurt anything? Anyone else having this happen?