if u wanna get the E93, do consider the inline 6s. they are less prone to failure and is generally well suited for the cabrio, which is about 100+ kg more than the coupes. if budget permits, 335 e93 is the way to go. ive test driven a few used e93 and the 320 inline 4 and even 325 is way underpowered for such rides.
usual suspects: transmission failure, air-con, water & fuel pumps, radiator tanks, hoses leaking. All these cant avoid, the rest see your luck.
happy hunting.