your denter is a crackhead.
any car needs fresh air intake for the cabin. The wiper tray area needs to be rebuilt because while people spend thousands of rupees on car washing at a service station, they spend zero rupees in cleaning this area and also door cavities and other drains.
by not cleaning out dirt, debris from here water gets stuck and slowly rusts the area. If you keep up with cleaning it, which is nothing more than vacuuming it or even blowing it clean with compressed air - it wont ever rust.
This area also needs to be sprayed with a generous coat of cavity wax every 10 years or so (just like the factory did), it already has channels for water to flow to the side drains which end behind the mudguard apron (sheet metal mudguard in desi lingo). Its a very old design and Im quite surprised that your repairman is not versed with it.