Hello, I am just trying to sort out my 1986 golf gti which I rally on HRCR events. There is a water leak under the bonnet from the heater return pipe. I note there is a second pipe linking the hot water in pipe to the hot water out pipe into the heater matrix ( I renewed this last year) which uses a smaller 6mm diameter hose. Does anyone know what this is for if I eliminate this pipe I get rid of my leak, I may just by pass the heater matrix for the summer. The problem part is a 3 way metal union I can’t see them listed anywhere …. Any suggestions appreciated.