I've had to replace a rear sensor - it give me a dash air suspension warning light which the code reader told me was a defective sensor (and which side). Easy to replace (buy genuine - there is a lot of junk around), I don't think I needed to erase codes for the light to go out - but it's been 4-5 years.

Based on the likely age of the car and air springs, as is the case with ALL of our E53's, consider that you have rubber that is under pressure. It moves and flexes a lot. It has to endure changing seasonal temperatures. It is logical to expect cracking and then leaks. Buy a pair of rear air springs from Arnott and replace them, just check if you have standard or sport suspension (get your build list from the BMW VIN sources - BMW archives - online). They are rather easy to replace - read one of my posts for some helpful tips. If you have issues, you can also PM me.

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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.