I have the same "problem" with my RB 300s. This is my second RB 300 by the way. The first one had that problem too, PLUS the azimuth was way off tilting my cartridge to the right, PLUS when you cue the lever all the way down, the tonearm only goes down midway ... you must only cue the lever midway for the arm to totally drop onto the record. Rega's QC sucks! (My second RB300 is okay though except for the "strong" antiskating - which I now attribute to be normal for all RB series tonearms).
http://img523.imageshack.us/img523/91/1000953cf1.jpg
http://img523.imageshack.us/img523/91/1000953cf1.jpg