| If you've set the lever assy correctly, then the problem is likely to be elsewhere. Did you check the condition/action of the stopper arm on the clutch side, as advised above? If both of these are good then the motor will need to come apart for further investigation. The gearbox, drum & selectors are pretty robust, but I have seen badly worn & bent selectors and that would account for the problems you describe. My concern would be that you say the problem is getting steadily worse and that would indicate that something is wearing. | 
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