01 subaru legacy

Head gaskets leaking oil. I am guessing your head gaskets are the culprit but for Subaru's this is common, way too common.

Hang on; might just be a burst CV (DOJ) boot that's splaying grease onto the hot cat conv. If not run 10w40 to see if it abates sufficiently to ignore. If not, check for source. If still running wet on the right side and you don't have to endure winter cold starts go to 20w50. If still bloody you'll probably need valve cover or head gaskets. But chase the cheap stuff first.