If you're the original owner you should know if it was replaced or not.
I think there is a thread with images of the old vs new filter, the new-style filter is longer than the original, they had to put a "loop" from the front port in the filter over to the pressure line to make it all fit, so you can look for that "loop" (should be able to find an image of the update lines as well around here somewhere, that should help).
The filter can normally be replaced by removing the left rear wheel, then some guys will wedge a block of wood between the inner fender liner and frame to get enough room to do the job. To me this is rather "butch" and I remove the inner fender liner, only adds maybe 5-10 minutes to the job to do it right. IF it needs the updated filter, that's where you need to R&R the left side of the rear seat to get access to the top of the fuel pump, so you can install these new lines. The pump is down in a depression in the top of the tank and no other way to access the ends of the fuel lines. There is a glued-in metal plate that covers a hole to allow access to the top of the fuel pump, this beeds to be removed. Same thing needs to be done to replace the fuel pump, which also is the part that needs to be replaced if the fuel level sender is bad, all one big part, not available as seperate components.
I don't think it's possible to buy the original fuel filter either, must be something made special for the ML and MB "shut it down" I guess you'd say on the original short filter. If I am wrong and the original filter is available somewhere, I'm sure others would like to know. Sure would make it nice to have the option. I am unsure why MB changed the filter design, other than the normal MB explaination "In order to continue superior service, occasionally modifications are made that will cost both Mercedes-Benz and the owners boatloads of money and if you don't like it TOUGH and blah blah blah haveaniceday..........
Gilly
Gilly