If I'm thinking of the correct pipe you are on about the smallish pipe that comes off of the metal pipe that runs along the bottom of the radiator and then goes into the side of the water pump on the engine,


I don't know about a RS500 but I have a pipe that is similar on my car and I obtained it from Graham Goodes, GG part number for my pipe is 1212,

Give them a ring they will more than likely be able to sort you out


Luciano