service records of the last time a HPFP or injectors were done. I work at a Ford dealer but decent friends with a few BMW techs. The warranty is important if you have one that is older or never had replacements taken care of. Ill be selling my 09 soon and I know that question will be asked hundreds of times till I sell it. Although Im not the original owner I do have all the records for mine.
When you drive the car listen for whatever you can.