you wouldnt normally loose boost. you might have a vac leak or blown a pipe. Is it defo bottom end knock and not release bearing or injector clicking? Get a vid up
Id send it of for a rebuild mate as second hand turbos are a nightmare. Half of people selling them dont know how to tell a working turbo from their dogs breakfast
Yeah it would have to be cnc machined, but you could use washer to get the desired gap then get the measurement to a engineering firm who could make you some.
hmm had a thought. could you remove the studs from the ball joint put a spacer between the arm and ball joint? Secure with nut + bolt and longer threaded bolt for the third? Just not sure if it would put too much directional stress on it.