I must say I might be a little biased on the reliability of the air suspension on the e53, maybe it's not THAT BAD after all as I thought, thanks for your insights!

After getting this really mint example of a 21 year old 3.0d my most important job is to make it as reliable as possible, changed all the front end suspension parts with Meyle-HD,did all the usual preventive Maintenance on the M57 3.0d engine and a complete cooling system refresh, an oil change on the ZF 6HP is planned as well.

I can work on the car myself and order good priced quality parts from germany.

To get the car as reliable as possible the SLS is still on the to-do list... I dont mind doing the work and buying the parts.

But now I am torn between leaving the SLS as is and replace an Airbag or a sensor here and there when the time comes or just convert everything at once to springs to have peace of mind.

Can a sudden SLS failure leave you stranded or are there always warning signs before that will happen?

As the car has the "Sport Susension Settings" (S0226) I would be glad to hear which OEM parts (dampers/springs) I could use best to achieve the same height and hardness like a car without SLS but with the S0226, will Bilstein B4's do the job ?