Hi, just bought a 2019 500x with 1 .3L engine. I searched to do routine mainetnance for many different products for my Fiat and noticed Severe Gear 75W-90 as offerings for my vehicle here on this site:
https://www.searchforparts.com/oil-change/fiat-2019-500x-1.3l-1-eyf-turbo

does that really need to be changed? of course engine/transmission/coolants/brake fluid, power steering, but the rear axel i think it is?

Diffs do not have to deal with combustion by-products and heat like an engine oil has to. So a diff oil can last much, much longer and some say "fill for life" but the gear teeth in the diff will always be trying to mash up the oil and shear it down (thinning).

So, it is good practice to change it every once in a while.

Cheers,

Guy