HEADER DEF QUALITY SENSOR for 2015 Freightliner Cascadia

Hello All,
I have a 2015 Freightliner Cascadia with 755k on the ticker. Thankfully I’ve survived my 1st year as an O/o Recently noticed a coolant leak under the drivers side door. Saw that the 1 of the bunk heater lines was leaking. Had a friend of mine cut the lines and loop them. Problem solved temporarily. A few months later starting seeing coolant again in about the same spot. While the truck was getting PM service I had the mechanic check it out. After a pressure test. He informed me that I needed a Def Quality Sensor. Price $1600!! I felt like a baby seal that just got clubbed over the head. Told him that this was gonna have to wait a month or two. The leak isn’t that significant. My question is does it have to be a brand new one? I looked online and saw several on E bay for like $450. Does it matter if it’s new or used? Please provide any and all feed back. It is most appreciated. Thanks in advance.