hi all,could somebody tell me where to get those rubber type cones which save having to drain down please.how much are they roughly?or is there a trick of the trade i think one of the olives is cranked on the radiator and would like to have a go at changing the valves without the b**lache of having to drain. i suspect its slightly risky anybody got any stories where its gone t***s up,waterfall styli?.thanks once again