I feel your pain too...
I went to the dealership a year ago and purchased brake pads and sensors for my 300E. Wanted to save a little money, since I've done that work on some non-MB models I've owned in the past.
Tackled the rear brakes (no manual or CD or anything), over-dissasembled everything (calipers completely off, brake hoses off, etc.). Couldn't figure out how to get the front ones off. Had air in the lines (DUH) etc.
Sheepishly took the car to the dealership and handed them the remaining parts to complete the job correctly. Probably cost more than if I had them do it originally, since they had to bleed the system also.
These were my pre-forum days. Recently got my hands on a manual, and could kick myself, as the brake pad procedure was far easier than I went about it.
I have had other "Homer Simpson" shade-tree mechanic episodes, but this would be a long thread if I elaborated on them...but I have gotten extremely good at working on my Beetle, simply because I screwed up so much! I expect to be fairly adept at my 300E as well...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car