04 X5 4.8 SELF LEVELING SUSPENSION PROBLEMS

[nitrogass2000]

OK, this is my first X5, and right now it has self leveling is inactive.

Dealer told me that my EHC Module is bad this part here

Part 37146773999 (AIR SUPPLY CONTROL UNIT) was found on the following vehicles:
E53: Details on E53
E53 X5 3.0i SAV
E53 X5 4.4i SAV
E53 X5 4.8is SAV

And also was told that my front air suspension is leaking. So, my questions are:

1. Where the hell is this module located? i could not find it for nothing! I know its in the back, where the spare tire is. But where is it exactly? Any one know? Also, where can i get this part at the best price, i could not believe my ears when they said it cost 850.00 at the dealer! Any used yards you can recommend? or a good new parts retailer?

2. I was told i can buy just the rubber "air bags" and replace them instead of buying the entire air strut. Dealer does not sell these things but i hear you can get them aftermarket?

Thank you all for your help!