Are you sure it's not the latch or the lip that the latch presses against? I had a similar problem on my ClassicIII, and it turned out to be the lip was worn out, so the tension fromt he belt lifted the nozzle and wouldn't press the safety switch, and hence wouldn't work...
I used a bent penny to wedge it together, not an ideal solution really, but it made it all work so I could test it... 
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