After much searching, I never saw a concrete answer to the differences between these two runs of the W126. So, for that matter, I would like to create a solid thread to leave for the W126 enthusiast.

Here are the basics:
1st Generation W126 ranges from 1981 to 1985, included.
2nd Generation W126 ranges from 1986 to 1991, included.

I have filled in some of these already, but I would like to have the moderator(s) compile everything down here in the following categories:

Seats (7-pleated design on 1st, big-pleated leather from 1989 on in 2nd).
-Underdash plastic key holder and rolltop console box in 2nd. (Standard on models with passenger side airbag, option on all others)


EXTERIOR
-Longer wheelbase (+L) models available in 2nd.
-Bumper design (vent design in the front).
-Lower plastic moldings (ribbed in 1st, flat in 2nd).
-Headlights (recessed in 1st, flat with plastic cover in 2nd).
-Headlight wipers (an option in 1st, standard in 2nd).
-"Bundt" wheels on 1st, 16-hole wheels on 2nd.
-Automatic heated mirrors in 2nd.
-Electric sliding sunroof in 1st, tilting and sliding in 2nd.
-Better rust-proofing from 1985 on.
-Water heated windshield with thermostat (2nd).
-Different dome light designs (seatbelt warning in 2nd).

INTERIOR
-Seats (7-pleated design on 1st, big-pleated leather on late 2nd as an option).
-Different seat motor design in 1st and 2nd.
-Airbag (option in 1st; driver's standard in 2nd, with passenger as option).
-Underdash plastic key holder and rolltop console box in 2nd (option w/airbag).
-Vinyl door panels (1st, early 2nd) and leather (2nd).
-RS seatbelts from 1985 on.
-Adjustable steering column.
-Electric headrests standard in 2nd.

DRIVETRAIN / MECHANICAL
-Differential subframe mounting configuration.
-Different window regulator styles.
-Frequency valve (1st) vs EHA valve (2nd).
-Gas: 380/500 engines (1st) vs. 300/420/560 (2nd).
-Diesel: OM617 (1st) vs OM603 (2nd, on 1986-87 and 1990-1).

BRAKING / SUSPENSION
-Smaller calipers on 1st vs. bigger ones on 2nd.
-274mm brake discs on 1st, 300mm brake discs on 2nd.
-Rear hydraulic leveling suspension in 560SEL models (2nd).
-ABS: option in 1984 and standard from 1985 on.

ELECTRIC / ELECTRONIC
-Memory seats (option in 1st, standard in 2nd).
-Deletion of radio aerial adjustment switch for 1991 only.
-Traction control (only available in the US in 1991).
-Third brake lamp, standard in the 2nd Generation.
-Low washer fluid cluster light only standard in 2nd.
-Low engine oil cluster light only standard in 2nd.
-Different Becker radios in 1st and 2nd.
-Different climate control systems in 1st and 2nd.
-Different headlight switch design (letters illuminate).
-Solid state transistor for blower motor.
-Recirculation mode in climate control.

Help me complete this list!

__________________
[GONE] - 1995 Mercedes E300 Diesel - 130k miles - Smoke Silver (702) over Mushroom leather (265) - Bladder blasting, coast-to-coast work machine.