See the discussion that CL420 and I were having on his possible purchase.
1992-very late 1995 are effectively series 1's (reversing prongs, oldstyle aircon controls) and badged as S500 and S600 (although have seen saw a purple S420 and a silver S420 coupe)
Very late 1995 - mid 1996 are series 1.5 (they have reversing prongs and no side airbags but the rest of the car is a series 2) they are badged with the S
Mid 1996 to end of run (late 98/early 99): they are the CL's - parking sensors, side airbags - rest of the car remains about the same
CL420 - fine car, great value for money
CL500 - that engine is just magnificent - my pick
CL600 - goes like stink but just waaaaaaaaaaay too much to go wrong over the 500 and 420 to justify the relatively small increase in performance
All of them suffer from rust around the arches also.