I sincerely doubt that the E-class declined in quality during the last years of production. My 1995 E320T wagon and a friend's E280 sedan still drive like the first day they were driven off the dealer's lot.
The problem is how the original owners take care of their cars. By neglecting it, a W124 can be trashed quite easily, they are not as rock solid as the W123s were. In the same way, a neglected W140 will feel and lock worse than a neglected W126.
If you shop around, you should be able to find a late model W124 that is rock solid and realiable (if the original owner really took good care of it).
CL 500, 1998
S 500 L, 1998
E 320 T, 1995