According to DriverSide, Replace rear drive assembly (RDA) fluid at 120,000 miles. https://www.driverside.com/service-...e-2016-1354625-3592235-9734071&mileage=120000 There is a lot of good "Renegade" specific information on this website.
The Owners manual says to check every 40k It also says you should add fluid if necessary but replacing the old fluid is not required. You would only need to replace the fluid if it becomes contaminated.
I just did my rear differential fluid (2.4L) at 37K miles and it was nasty looking. Before I drained it was quite a bit below the recommended level mentioned in an earlier post, and there were no leaks, so I can only assume that it was underfilled at the factory. Service manual says it holds 20oz. I drained 15 and refilled with 16. It is now 6mm below bottom of fill hole. I also did the transfer case/PTU. That fluid looked much cleaner. Manual says 13oz. I drained 10 and refilled between 11 and 12. I used Amsoil 75w-90 Gear Lube but any synthetic 75w-90 with a GL5 rating should work. I don't buy the "fluid for life" thing. Never did.