DRT cluster inner needle bearing too small to cope with 21 needles

Hallo zusammen,

I've been trying the whole day long to understand why my new DRT spitfire cluster couldn't accept the 21 needle bearing. Brand new shaft (an old one too for comparaison purpose), a complete set of sip needles (2/2,14mm, those for PX...) and nothing. I just can't shove in place the shaft surrounded by the complete set of needles. Beyond 18 there is not enough room.... I've never had such an issue... I've compared 2 clusters and obviously inner track of the drt's has a smaller diameter than a standard piaggio's cluster. What can I do?