Ok had a search cant find anything specific, How can I tell if my universal joint is worn?

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wiggle the shaft back and forward and see if there is any slop.

easy to tell if the uni is worn.

open the drivers door, sit in the seat, crane your head down and to the right. If the odometer reads over about 100,000klm the tailshaft uni is worn

or you could try moving it back and forward like CeJay suggested but that sounds harder. You will also feel it through the drivetrain when you get on and off the power at low speeds as a clunk (although this could also be poorly adjusted diff centre, or worn gearbox mount.