Tried to install the rear differential into my X5 (Vin:L098986) and the rear differential I was sold by my former mechanic is too small it appears. The axle splines do not click into place.

The one I pulled off had number of:
75230940 engs40015

The new one has number of:
026 23908
7553948
engs490-15

What is the difference and what do i order?