2004 Kubota 3130 leaking oil from drain plunger

[cyclepainter]

I have a 04 3130 4wd with a DT trans. 209 hrs. that just started to leak oil from the drain plunger which is located about mid belly on the tractor. my local dealer says it could be a seal from the engine or 4wd. It is a dark , not red, colored oil. It only leak about a 2-3 inch circle after I use it and load it on the trailer. I hope this is a warrenty item, but has anybody ever had this problem?