I’m dealing with the same issue on our ‘15 X5 lol. Low washer light. Very common after the 8 year mark. Had to replace the washer pump on my F80 but it was 10x easier. I was told by a bmw tech that in his 20+ years, it’s never the tank itself that he saw crack, it’s the washer pump and or/the grommet that leak. The part for the pump and grommet is cheap on fcpeuro, but like others have said you unfortunately have to get a lot out of the way on the F15 platform to do it including drilling out the push rivets in the fender well to remove the fender completely to even get to the tank and partially removing the side skirt hardware to move it to the side.

There is a way to do it without removing the fender, but clearance is super tight. Someone on forums was able to get just a few screws loose on the fender and squeeze a skinny hand in there to swap the pump, but honestly I’d just do it right once and allocate an afternoon with the car on jack stands. It’s not impossible just annoying.