I don't know that 90-92 CIS cars are problematic really but it seems to me wise to get a 93-95 LH car. The later EZLs are are less likely to be trouble and the diagnostic system is considerably better. 1993s were called 500SL and 94-95s were SL500s but they are all the same car, and they're not much more expensive than the 90-92s in comparable condition. 1990 to 1993 offered more colors and more interesting color combinations - everything started to get bland in 1994.