Contact your dealer or American Honda and get on them. I too had the exact same problem with mine, a crack in the plasastic in the exact same spot. I got a hold of my dealer, then got corporate involved. They ended up paying for a new OEM aluminum radiator geniune honda parts. They also covered labor. I just got on them. I wasn't rude or anything just firm. I explained my situation and explained to them that under normal operating conditions the radiator shouldn't crack and as you agree plastic should never have been used. Honda is generally more than happy to assist its customers in these situations.