MB approved bodyshop require main agent or only MB authorised garage to approve your claim (so take all your docs as they will take copies) this
HAS to be ratified by ESCO labs prior to MB repairer undertaking repair on your vehicle.
Watch out for service manager saying your corrosion is due to stone chips etc when corrosion is due to poor materials/processes, check other parts of the panel for corrosion. Lift up rubbers etc and check inside boot areas etc etc as if corrosion is in one area it is likely to be found elsewhere. When repairs are carried out it is best to get them all done at once as opposed to repeat visits as paint fades and your pride and joy may resemble Josephs dream coat by the end.
Don't be afraid to disagree with MB, ESCO labs, dig in stand your corner, get copies of information and pictures sent inc dates before it is forwarded for approval. The garage will be notified by ESCO labs re: repairs in a matter of days (2-3) concerning approval or not so do not leave awaiting a reply keep on their case.
There is no real money in corrosion repairs for the agent or bodyshop hence lack of motivation to get things sorted at some garages hence you being fobbed off and rusty cars are not good adverts on their forecourts.
For corrosion do check seams, paintwork edges, underneath panels if you can or if you can get the car in the air on a ramp thoroughly inspect the car or get an independant recognised, competant, qualified, body shop (preferably using a snake eye camera for awkward inspection areas) to undertake a producing a report on your behalf as MB approved repairers get paid a set fee for repairs based upon set MB time scales per job which work out to be really tight time scales for repairers so quality may get missed hence the number of posts about reoccurring corrosion. Do not accept second rate work, when they take the car record the mileage, fuel guage, and ask for a courtesy car, and v. important obtain a copy of the work to be done (like when you collect/deposit a hire car) as cars can suffer damage whilst in the hands of a third party and any evidence you have to corroborate damage incurred whilst the car is not in your possession is power to your elbow for getting them to return the car without additional damage being incurred.
If you are unsure as to recognising the quality of repair completed take with you a bodyshop trained person to inspect your car as when the car is returned as they will see faults a mile off which an untrained person may not.
Good luck perseverence pays.
Chris