enginedriver

My 2008 RX400h with 135k on the clock has started to lose small amounts of coolant from a hairline crack about 100mm long I have spotted in the plastic plenum chamber (I don't know its correct term) which is the only visible part of the main coolant radiator. By small amounts I mean enough to take the header tank from max to minimum in 2000 miles - clearly however it might get worse.   Lexus are quoting £800 for a replacement radiator.   Does anybody have any suggestions of glues or whatever which might do the the job?

With Noah busy on his Ark. Does anyone know or has any one tested the wading depth of a RX400? I got through nearly 12" last night without apparent trouble which is about up to the wheel bolts.