Can you tell me if it 's a critical area (Dangerous for the structure) can it'll be easyly repeared?

In my opinion, it is a critical area because it is part of the body that takes suspension stresses. There are 2 panels that gradually curve together to be spot welded at the bottom of the spring tower. I had to cut out the inner damaged panel (in the engine bay) and weld in a replacement.

After all is repaired it is essential that all seams are cleaned, treated with Metal Prep (phosphoric acid), primed with etch primer, THEN sealed with a good quality seam sealer.

It is the wheel arch seams that MUST be absolutely water tight.

Follow with primer and top coat.:classic:

A big mistake that the factory made (makes?) is sealing these types of seams BEFORE treating the metal.

Then, as you could imagine, it is only a matter of time before the corrosion works its way out. :tapemouth

thanks for your reply!

The car i purchase have the rust in the middle of the spring tower, just behind the middle of the spring, my idea was to cut the rust area (10cm/5cm) and patch with a good metal job, and treat befor and after weld, with a phosphasting rust removal, and after, treat with phosphating primer.

What did you think about my idea

Sounds good to me.

I am a staunch advocate of replacing rotted metal with new metal.

NO FILLER TO MAKE IT LOOK GOOD.

Filler is only for a difference in levels or deep scratches etc.

Also there is the problem of structural components and in a unibody, IT IS ALL STRUCTURAL!