Thanks alot GREG891
.including all other folks who have shared
their inputs, your comments are truly appreciated and busted my confidence
to move forward now by replacing the two rear air spring bag.
However I do Not have any (self level suspension message) N'less the car
was parked for 24hrs on an uneven surface without moving, & from there
the message will appear at the 1st start-up, but will go away after the car
finished reaching it's normal heights.
Otherwise, I'm glad that you have endorsed the (Arnott Spring Air bag)
because I was looking at the (OEM Spring Air bag on Partsgeek.com)
and they run for: $200 each side.
I will keep you guys posted on the outcome...
(01 X5 4.4i E53)