Usually 75-90W. I personally went to a synthetic differential oil. I will not extend my change cycles, as the cost is so minimal. I just like the extra protection, and have been told by those that did 'before/after' infrared temp readings, that the differential run cooler.
If in doubt, call CC with your coach build number, and they should be able to tell you the exact differential you have in your coach. Go with what that manufacturer say's is the proper weight. (You might look to see if our documentation package includes this info.)
And good for you doing this. I've been so surprised over the years, by the number of owners that have never changed their differential fluids. Out of sight, out of mind!
Roo II is our 04 Country Coach Allure 40'
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