Heater Supply Hose
I have had the same issue with the 'Y' connector leaking - a very poor design which should have been aluminum... You cannot buy the Y separately, but will have to buy a bundle of hoses and aluminum tubing for the heater system. The part number is: 4677603AK and I believe it is called a Heater Supply Hose. It is $96 + tax and you should be able to install it yourself - I did that and it took about 20 minutes (did not replace the aluminum tubing - but replaced the two Y connectors including hoses). Remember to buy a bit coolant fluid as you will lose a bit when replacing the tubes.