I had my Volvo muffler done at Can Tire.They last 1-2 yrs each time.So I had it replaced 3-4x since 5rs ago.The muffler replacement and labour is free.
But they charge for pipes,hangers etc and associated labour.All in all,as Volvo dealers also guarantee their mufflers for life,I lost money using non-Volvo compared to if I had used Volvo original.
Now because MB doesnot give lifelong guarantee on their mufflers,only a miserly yr,I was told.that's a different story.

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Tom 1992 300E 2.6