The 3.0i was marketed as the 25i and 30i. Identical engine, although configured differently at the factory and equipped with a distinct intake manifold.
The N52 utilised port injection and was regarded as highly reliable; nevertheless, it is ageing and requires numerous component replacements.
The N53 was BMW's first direct injection engine and represented a significant advancement. Concerns include the NOx sensor, NOx catalytic converter, injectors, and high-pressure fuel pump. These are notorious for malfunctioning, and the repair costs can be substantial. I have observed individuals acquiring discount N53 vehicles, only to later lament on forums about engine misfiring, with mechanics stating that six new injectors are required. Conduct extensive research prior to making a purchase.