I replaced the copper injector seals on my new to me W211 ('06 E320 CDI) after an episode of Black Death did it's deed.
Afterwards, I noticed my MPG dropped what I'd call significantly.
I went from 42 on the freeway @ 75MPH to 38MPG.
Around town average dropped from 28 to 24MPG.

Hence, this post...
The o-ring replacement was fairly straightforward.... slide hammer injector removal tool to remove injectors, installed bolt to correct torque value.
Only one hiccup:
Removing #3 injector, I didn't control the removal and it came out about 6" and landed on it's tip at a 10º angle on the aluminum head.. I couldn't see or feel any damage whatsoever... so I reinstalled it.

No smoke, codes, idles perfectly, doesn't feel as if one cylinder isn't pulling it's weight.... you get the idea. I didn't drive it enough before the repair to form a strong baseline for MPG so I don't know if my numbers are common or not. Honestly, I expected more power and better mileage as I was banging out 50MPG with my '03 Jetta TDI. I knew I'd get less - but half seems ridiculous!!

Any recommendations, instruction, ideas, or info would be appreciated.
I'm very mechanically apt but have little diesel experience. What I don't know, I can follow in a manual.

Thanks, Jay from San Diego.