i wouldnt worry about entry level 3 series in terms of reliability... if you are a car person you just do what you have been doing then you are alright... (aka change oil 3-5k with premium synthetics, keep up with coolant changes, all fluids should be swapped every 2 years etc. etc.)
i bought my preowned bmw x3 (my other car) without looking at the history... some person traded it in and i picked it up at an audi dealership
but then again, i have owned 5 BMWs already in my life (25 years old) and i know what to expect going into owning a BMW...
the second you buy it, take it to an indy and have them change coolant, brake fluid, oil, trans fluid, diff oil...
after that, you should be fine for a while












