HI, I have a BMW 520d E60, 09/2007 and have issues with the DPF system. Namely, there were several error codes on the computer diagnostics. I replaced all four glow plugs and the module for their activation, the lambda sensor, both thermostats (the main one and the EGR thermostat too) and cleaned the DPF both from sooth and ash (at a BOSCH professional service). The car managed to regenerate, however, after some time it started throwing the error codes DTC 4667 and DTC 4D00. I also noticed that the oil level started rising. I found on internet that the first code means that the car was is trying to regenerate too ofteh. After deleting the codes and driving on highway, it seems the car regenerated again. But after some time, the code 4D00 popped up again, the oil level started going down (even below the minimum) and the car lost its power. Also, a weird grinding sound comes from the exhaust system and my mechanic says that the DPF is clogged again. I bought new exhaust back pressure sensor, assuming that the current one could be faulty and giving wrong info to the computer that the DFP needs to be regenerated, so after many attempts to regenerate the DPF indeed gets clogged.

Could my theory be correct? If not what else could be in question? Thanks in advance for any useful advise.