2003 325i thinking about it

looking at a 325i 43000 mi $18,000.00 is it worth it? any common problems? ball joints, engine, trans., electrical or anything else i need to know? i am a first time BMW shopper and i do know that maint. cost is much higher than my Bonneville. my Bonnie is in perfect condition 65,000 miles and still going strong should i keep it or go BMW?