Same thing happened on my D2a over Christmas and I've seen another one with the exact same centre crack as well.
And to top it all off I took Lady P in for a service to get the radiator cleaned this week as she was running hot above 35 deg ambient temp. Plastic side tanks were brittle and cracked up on removal. As its a special design this means a new radiator :mad::mad::mad:
So less said about plastic,durability in cars these days the better.
Cheers
Steve

