WRX SCOOBY

lads there is a rattle from the wastegate and when held at a rpm it starts to jump like the waste gate is opening and closing and it doesnt know wheter to boost or not ,,its ment to be the bushing in the turbo that holds the wastgate is worn ,,,how do i fix or what do i do thanks ,,,,also will a 94 turbo fit a 99 block thanks