The 124 chassis with the 603 motor is a much more refined car than the 123. I have both and can tell you they are both great but also different. I prefer driving the 124, especially on the highway, because it is faster and much quieter. Around town there isn't as noticable a difference except for the power and slightly better smoothness of the later car. The only real negative I can tell you is that the 124 lacks the solid, cut out of one block of steel feel that the 123 has. I'm sure you've read about the cracking head issues but if you find a good car you'll probably be pretty safe.

My 124 has the trap, all the California cars did and I'm not sure but I think all US cars in '87 did too. By now they all should have been retrofitted with the catalyst. If you find one with the old oxydizer still on it be careful, it doesn't speak well for past maintenance, especially since the retrofit was/is free at any dealer. Prior to 1987 it was just California that had the traps.

As luck would have it, there is a decent looking '87 with 150K miles on EBay now. One of the photos shows it on a dealer lot with a $7999 price on the windshield which I'd guess is a bit high. I recently bought mine, a rust free California car with excellent interior and 105K miles for slightly less than that. I don't think I got a bargain, just a solid car at a decent price. While there aren't a zillion of them out there you see them from time to time.

Hope this helps. Good luck with your search.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold