I've only dabbled with the hydraulic version on the 1000 engine but I would say the cams/worm and or balls inside there are worn out. 33,000 miles exposed to all the dust, grit, salt and water the drive chain drags in and throws at it is perhaps enough. Might also be surprised just how heavily loaded that little thing is.
Genuine new Suzuki will be around £50. I doubt a used one could be trusted unless it came for next to nothing.
Assumed you checked the handbook to see if there is any advice for correct adjustment before you go spending. Might simply be that all adjustment has been made at the bar lever end all its life. Backing that right off and taking allmost every bit of free play (book will say) up with the screw and lock nut in the middle of that cam might find you the less worn parts to get you by.
