New Miraphone Rotor Not Fitting Properly

[Polkahero]

I recently ordered a new Miraphone 186 fourth valve rotor to replace a non-native rotor in a tuba I just bought. I can insert the new rotor but the paddle linkage won't fit on the stem as it's too tight. Also, the rotor doesn't spin around easily in the casing like the other rotors. Is there anything I can do myself or is this a job best suited for my local brass tech?