when i had mine out for this reason, i noticed that the ball (at the bottom of the stick) needs careful positioning to go back in there properly. also, it's not inconceivable that some debris, such as a little bit of rag or part of the old bushing cup, could have gotten into the transmission and would need to be fished out if possible. the retainer cup also needs to be reassembled properly onto the stick, or shifting becomes a mess.
basically, (have him) take the thing apart again and make sure that reassembly goes properly. did he use a marlincrawler bushing kit? did he mention that anything went together either 'too easily' or 'fought him'? if so, both conditions indicate a misfit.