Congrats on the GC CRD. My wife and bought ours 2 years ago with it having 11k miles on it.
Please make sure you do the following to your GC CRD:
1. Upgraded intake!!!! The original intake will leak oil from the PCV (CCV) onto the swirl motor causing its eventual failure. Swirl motor replacement is at least a $2-$3K job. I believe the bad intake has an orange flange at the air intake assembly connection to the turbocharger. The good intake has a black flange.
2. Reducing oil in the CCV system is important to reduce risk of oil leaking on swirl motor and clogging the EGR system. I have used a Provent system on my CG CRD since it was new to us. I collect about 9oz of oil in it between oil changes.
3. Beg, borrow, and steak the money for a tune. Although I had a bad experience with Immotion's customer support, I will tell you that their hottest tune kicks donkey. I'd do an immotion tune again but I would next time send my ECU in instead of trying to configure their hardware to my computer system. EGR cycle is supposedly reduced with the tune.
4. Do some homework on DPF regeneration. You will notice a regeneration when you are at a stop with vehicle running and smell a smell of "plastic burning"....if you do notice this, do not turn off your enigne and try to drive on the highway for at least 15-20 minutes. Repeated city driving with little highway driving can cause premature DPF failure. Highspeed/hard highway driving will allow for a passive regeneration (high exhaust heat from hard highway driving will cause carbon entrapped in DPF to burn off naturally...and constant highway driving is perfect for an active regeneration of DPF...active meaning engine injects diesel into cylinder during exhaust cycle (when exhaust valve is open) so it can migrate and ignite in the DPF causing it to regenerate. A new DPF is about $2k.
5. Mobile 1 ESP or equivalent is the only oil you can use. The oil you use must be DPF compatible and meet Mercedes Benz Spec 229.51. Using non emission (DPF) safe oil will cause DPF to fail prematurely.
6. There is a tuner in Europe that sells a DPF delete tune. It is about a $1000 tune....1/2 the cost of a new DPF. I've told myself that I'd get it as soon as my DPF failed but I actually like having an exhaust so clean I can stick my finger into the exhaust outlet wtihout it getting dirty.
7. Please consider some sort of fuel lubricity additive. I optilube XPD for my GC CRD and 2 stroke oil in my Liberty CRD

8. Air filter on the GC CRD clogs within 12k miles. I replace mine quite frequently at shorter intervals. Air Filter should really be twice larger in size at least.
9. Fuel filter is puny...I'd change it every 10-12k miles or sooner if your fuel quality is poor....Wish I could find room for a RACOR for it.
10. VERY IMPORTANT or you risk engine damage (main bearings damage). ON OIL CHANGES, 1/2 OF THE 10 LITERS OF OIL IS POURED DOWN THE OIL FILTER ASSEMBLY AND THE REMAINING 5 LITERS CAN BE POURED INTO ENGINE CONVENTIONALLY. I'd still wait 20-30 minutes after pouring oil into engine to start it. Do you think a shop or dealership has time to waste to pour the oil correctly into the engine?