The AUX fan in SOP will run for as much as minutes after the vehicle is shut off. Some people throw out FSR/FSU as the reason for every AC woe. It's like an automatic reaction.
The TOTAL charge for the system is just under 1 can from all accounts. If you need to recharged then you must have a leak. I had to replace the Service Port (High & Low) seals some years ago. The OEM seals were revised and a kit issued for older models so that standard "O -rings" can be fitted from then on. Cost was $11 per port or so then.
I took it to an AC repair shop. They found the leak and installed the new seals that I supplied, vacuumed out the system and recharged everything with the proper amount of "freon and oil for $95. Worth it when you consider the price of other parts should the recharge be done wrong!

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2021 X5 xDrive40i
2015 X5 xDrive35i MSport
(Traded) 2013 X5 xDrive35i