common for the head to crack on these, they don't often mix fluids.
edit, thought you said L200
start with a new cap, boiling point is significantly higher under pressure.
edit, thought you said L200

start with a new cap, boiling point is significantly higher under pressure.
need a part number? http://public.servicebox.peugeot.com/ and http://service.citroen.com/ will sort you out.