Mazda 929 auto drive shaft vibration uni joints renewed and drive shaft balanced Still have drive line vibration?

Had similar problem. Took it back twice to same mechanic still vibrating. Took it to another mechanic and he found that the old uni joints were still in place. The first mechanic from salisbury adelaide, welded washers in where circlips were meant to be. All had washers welded. New mechanic replaced tailshaft with seconhandy and did job properly, It is better than new now.