I am tempted to apply Turtle Wax Express Shine Spray Car Wax at the valley in this picture (where water that came through the gap between the main body and trunk hood flows. The red circled area.).
This part is not as clean as the outside exterior even after washing the car. However, I am tempted to think that spraying wax here will prevent corrosion.

I am also tempted to spray the wax underside of the car. The underside of the car is not so clean and I am unable to buff there with polishing cloth.
But I am tempted to think that the wax sprayed there (I will not shine because it is not buffed) will prevent corrosion and oxidization on the undercarriage.

I would like to know whether spraying Express wax is recommended in such areas (Not as clean as the washed outside body panel. Hard to buff.).

What about spraying Zymol Detail Spray (it is less than usual wax. it is inteded to enhace shine and protection on already waxed surface.) on such area?


(My car is 1992 Mercedes W124. The picture below is Audi A4, not my car.)

Attached Thumbnails

 

How about a nice rust-proofing done on the car?

__________________
99 C43
98 S420
99 C230K
01 C240

My 1992 300D's Mercedes-Benz Car Care Guide mentions waxing (applying Gloss Preserver), alloy wheel care, chrome preserver, and so on.

It does not mention rustproofing, or undercoating. Do you think there is reason?
Is rustproofing or undercoating developed after 1992?

I also saw detailing pamphlet of an MB dealer. It does not mention rustproofing.

It just mentions hand wash, hand wax, clean & dress wheels and tires, multi-step wax (compound, glaze & wax).

I just talked to an independent body shop.

They say rustproofing costs $250.

They also mentioned that if I already see rust on hidden corners, edges, etc., it is too late to apply rust proofing. They say rust proofing will not help much.

The picture below is my car.

Attached Thumbnails