i have a 435i with 27000 miles on it and was told I need to get my xdrive serviced.

I honestly do not see a maintenance requirement for transfer fluid or differential fluid for a BMW 4 series. However, the fluid should be serviced, and I do not think it's a bad idea. For more real-world local service recommendations, maybe do a search here on repair shops for BMW near you that can give you first hand advice: www.repairpal.com/repair-shops