Quote - If there are to much very little polygons, then i should be able to solve the problem with a weld function and the right distance value for it !

Be careful doing that. It would be easy to make a mess. I prefer to tidy up a mesh manually - it takes more work (although this is minimised by working on a low polygon version to begin with), but will give much better results.

Can we see a flat lined or smooth lined view, preferably a close-up of the area you're having trouble with?