Can someone look up the book hours listed for doing a rear differential swap out on a 1988 300 SEL?

My buddy needs his replaced and they are telling him 5-6 hours labor, which seems excessive compared to some of the DIY stuff in the driveway with a jack I've read about on here. It seems like a modern shop should be able to blow through that kind of job in hardly any time with all the fancy tools.

Any ideas on where to source a good used one?

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(2) 1988 300 SEL W126