Try these guys out for turbo rebuilds they offer free return shipping:
Turbo Rebuilding Services - XSBoost Turbochargers

To perform a quick test on your turbo, remove the curved plastic elbow connecting from the air filter to the turbo. Once removed place your finger on the turbine shaft nut and see if you can wiggle the turbine wheel up and down side to side. The less wiggle the better, new/rebuilt turbos has a nominal amount of play. Used turbos will move a noticeable amount.

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Nosce Te Ipsum "Know thyself"

Try to move the nut/wheel along the shaft axis as well. A hair of radial play is normal, any axial play is bad.

Sixto
83 300SD

They are so easy to rebuild, the hardest part is removing the turbo itself. Get a good rebuild kit, no specialized tools required except maybe a crows foot and extension. Clean real good and reassemble. You can also check the waste gate valve with very low air pressure. I now have a 1000 miles on mine and no problems.