pumba

Today I had a bit of steam coming out my front grille whilst sat in traffic, so i pulled over and inspected there was water ontop of the rad and also remnents of water sprayed over the engine, it looks as if its come from the top centre of the radiator. There was very little loss of water, I managed to get home without being stuck in any more traffic, I left the car running on the drive to try and see where the water was coming from, but nothing, I couldnt get it to replicate the problem. Has anybody got any ideas what could of happend or is there a common fault where the radiators have a problem?
Its a 2001 bug eye.

The only thing i did manage to do was to snap the rusty bolts holding on the air intake So got to drill them out tomorrow


EDIT:: Found the problem, there are some small hairline cracks on the top black plastic between the main centre pipe and the right hand side, so now its time for a new radiator, any ideas on the best place to get them from?