You are correct on coatings, Mercedes went to water-based paint in '92 IIRC, and clearcoat was not used on these cars unless metallic or black. Early ones only metallic / not on black.

The zinc (zink in German) dip was after all of the welding, entire 124 sedan (and coupe I believe) went through the zinc bath, the wagons for some reason did not get the same treatment.

The early 124 process was (excluding wagons):

Assembly/welding
Zinc phosphating with chromate rinse
Cathodic electrodip primer
primer
color-matched primer
color coat/top-coat
(metallic only) clear coat

The fenders and trunk lid were installed prior to step 2, doors and hood not added until after primer.

One big difference between pre-plated and dipping is that the zinc is breached at welds and the steel is more susceptible to corrosion at those points, the surface must be converted and sealed. Much of the rust issues that I saw on '90s Mercedes cars (mainly W202 and W210 but also my '94/'95 E320s suffered) are cosmetic at first, starting at areas like the body holes for the side-cladding clips, and when neglected enough become serious. The W210 spring-perch issue is of course different, and I don't believe completely related to rust (a good friend had his '99 fail, the car was never rusty, never driven in corrosive environment, never near a coast or driven in winter/salt, never even in an auto-car wash) but it is often attributed to rust and is perhaps accelerated by rust.

Oh, and the 124 used HSLA extensively in the body, IIRC it had over 30% high-tensile steel in the structure which is what led to its 54hz chassis resonance (extremely stiff for its time).

__________________

Gone to the dark side

- Jeff