1985 diesel mercedes downpipe removal

Hello,
Went to replace my downpipe because it kept allowing my muffler to fall down due to it having the last four inches rusted off... and the bottom of the three bolts holding it to the turbo is rounded off. How can I get it off? I put the other bolts back on thinking it might have binded it up but no luck. Also tried heating it, and WD40, but its too far rounded. I also though I could take the two studs I was succesful in removing the bolts from and then just hammering the downpipe in a circle back and forth until it loosened but one is too close to the engine to remove it. Am I taking it to a repair shop to have the turbo removed, downpipe attached?

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