Dunno about your model bud but on my C220 a faulty fuel temp sensor caused strange loss of drive with no emls or anything. I only know it's that because when it finally did go anfd I had it replaced the issues went away.
I think as said, at the age/mileage/value etc and bought from an auction I’d not lose sleep over a 30/40k mileage discrepancy on a 13 year old car. I guess it’s showing circa 130k now rather than 160/170k or something?
If it were a 50k miler 5 year old car for say five figures that turned out to have had a significant haircut and you’d bought it retail from a garage then it would be worth pursuing but at this age/value there’s little point in worrying. You’re unlikely to have overpaid massively at this stage it would have been the person who bought it with ‘98k’ on it who’s been stung worse IMHO.
Look at the positives - you say you’re happy with the cosmetics and it appears to have full history with MB up to 130k. To me that indicates that the car was well maintained up to that point and if it’s otherwise a nice car just get the power issue sorted out and enjoy. I doubt it’s in any worse condition than most other 2006 cars with average (ie 100k+) mileage
You will have the OM642 engine. I am slightly unclear which form of NOx exhaust treatment you will have? How the Mercedes-Benz BLUETEC System Works?
On older Mercedes diesels its often the anti-emissions kit [ engine or exhaust located ] that breaks down at high mileage. The auto transmission also talks to the engine management system so a transmission problem may also cause the car to go into limp home mode.
ps owners on a budget tend to get rid of older cars in decent condition, only when faced with a repair of significant cost , otherwise they hold on to them.