97 c3500 dually 4x4 differential oil

Hey all,
I got a question maybe someone can answer. On my 97 3500, I was having the oil changed at the local super lube place and they asked me about
having the rear differential oil changed. My truck had 36,000 miles on it and they told me that the original oil that came in the rear differential was only for break-in purposes and should be changed at 5,000 miles, and replaced with a different type of oil. Call me a cynic, but I've never heard this before, so was wondering if he was just blowing smoke up my butt trying to get an additional service item, or if this is actually true. I bought the truck when it had 24,000 miles on it, so it might have already had that oil changed if that is truly the case.
Any ideas.
Thanks,
Kelly Lee
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It honestly sounds to me like they are full of something.

case.
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they told you wrong............ I've never heard of that
On Thu, 31 Jul 2003 04:48:17 -0600, Kelly Lee

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