I would get a second opinion. I have worked on loads of auto AC units and
have NEVER seen an evaporator ever even begin to rust out. I have
however, seen loads of bad "O" rings at connection points. I suggest you
put some R-134A in the system and spray all connections with soapy water.
Remember you have gas and oil circulating in the system so don't forget to
add the correct Honda refrigeration oil to your system after the leak is
repaired but before you evacuate the system and add freon. When freon
leaks out, so can the oil. You also might be able to find the leak by
finding an oily connection on one of your AC lines. Good luck!