Given the age of the car, and the symptoms - replace both bags asap with Arnott. I did this (proactively) when my car was about 12 years old, with notable rubber cracks (fortunately no leaks at the time).

Our cars age, rubber flexes and ages. Add the air pressure on air springs along with the four seasons of temperature changes - this isn't a surprise. Consider an air springs as a maintenance item after a certain number of years.

Having replaced a LOT of shocks & struts over the years, fortunately replacing E53 rear air springs is easier. No spring compressors to deal with.
Do remember to pull the fuse (trunk fuse box) before you start, replace it when you finish the hookup to let the compressor replenish the system's air BEFORE you lower the car to the ground.

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2002 Euro X5 (E53) 3.0 diesel (M57)
5 speed manual with UUC short shifter.
Pre-xDrive NV125 transfer case (chain & gears).
Factory Xenon headlights, Spyder LED tail lights
Updated vortex crankcase breather.
Motorsport dead pedal, factory fire extinguisher, factory first aid kit, factory F&R mud flaps, factory PDC

Bilstein B6 shocks F&R
Redline oil has replaced "lifetime" fluids (F&R diff, manual transmission, transfer case and P/S).
Dimple magnetic drain plugs in all compartments.