You can call for warranty, if its less than a year, or you can dis-assemble, and clean yourself. In the pic, The bottom fitting may be leaking, but the top show signs of at least a past leak. You will have to take the top finger nut off anyway to get to the fitting that threads in to the header.
Temp sensor will more than likely give you some resistance when disassembling. Be patient, finger nut is the only thing that holds it in place. You can use a pair of pliers to break finger nut loose only! after you break it loose, fingers only. DO NOT grab the temp sensor itself with the pliers in an attempt to remove it from the fitting, you will only wreck the sensor. Don't forget to use some sort of NON-petroleum based thread sealant on the fittings' threads.
Assemble fitting into the header first, then slide temp sensor through fitting, then the finger nut onto the fitting. Finger nut should be on sensor BEFORE you slide sensor into the fitting. Bottom fitting should be finger tight and then about a half turn, probably wouldn't go more than one full turn if you have to. Top finger nut should be only finger tight.
Calling warranty gives him the luxury of having a temp sensor to replace with in the event he breaks the old one during removal.
Good Luck!