Rear diff fluid change?

I bought redline 75w-90 oil for my rear diff on my 2009 e90 lci 328i. I took my car to my mechanic to change a couple of fluids including the rear diff. I got a text from him today stating " diff has no drain plug so its not meant to be serviced." Is this true? I find it hard to believe that you can't change the rear diff fluid. I searched for a couple DIYs on servicing the rear diff but several of them stated "2007-2009 328i rear diff fluid change." Are lci cars rear diff different? Can you not service a 2009 e90 328i rear diff by draining and refilling it?