I'm having the same issue. the 25mm tube fits in all the parts like a dream except on the middle ends and middle joiners. i took the whole Z assembly apart took a middle end, and took the nuts of the bolts so the bearings were just sitting on the bolts and the pipe then went on but it was still not moving smoothly on the tubing. Took a 8 mm drill bit to the the 3 bearing holes, as the holes i got out of the printer the M8 bolt dose not go true nicely i have to screw it in, so drilled it out now, the bolts go in with no screwing needed and it moves a better but still not as freely as i would like or to say not as freely as the rollers move or the Z axes, those just glide. If i push the rollers they glide on the rail if i push the middle end it stop as i let it go, but it did want to fall down when i put the tube vertically and but i had to nudge it a bit and it fell for cca 10 cm before it stopped again
Now im thinking of drilling the holes out with a 9mm bit but scared that the hole will be too big and that the side bearings of the middle end or joiner will start to rub on the sides of the parts as now there is just a mm of space in between. Have you maybe put the American parts in the IE package :) ?