I’m confused by the terminology “rear” AC filter. Did they give you a part number for this filter because I’m not aware of a rear AC filter used in the f15 X5…even if you have 4-zone climate…or 3rd row AC. This is not to say I’m right…I’m just unaware…and can’t find any rear AC filter in the parts database.
There is the "set" of micro-filters that are located at the rear of the engine bay (perhaps this is what they meant by "rear")...which is item
#1 in the diagram below (only one is shown in the illustration but there are TWO filters sold as a set):
Then there's the re-circulation filter (item #2 in both diagrams below) which is used if you have the 4-zone or the IHKA AC system:
The diagram below is for the 3rd row fan (system)...its in the rear and there is no "filter" listed:
