2003 W209 CLK, 2005 R171 SLK, Volvo XC40 P8 Twin Motor Pro EV
With a 2001 C Class a 2mm hole is very good. They are usually much worse than that! Rust kiiler and filler will be fine but it will be back sooner or later. Sorry to sound so negative but its just how they are. Very difficult to stop it returning.