Is there a way to test & clean wastegate '85 300TD?

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Greetings. I have been struggling with trying to get my '85 300TD 157k back to proper running order. I am guessing the turbo is not operating properly as it used to produce a little whine when it ran better- and it stopped doing that some time ago.

A mechanic suggested to check the wastegate to see if it might be stuck. I am hoping someone can provide me with some steps on exactly how to check that and/or how to clean it out.

Thanks as always guys!