yes @Invisible i did sort your one out. plus your whole loom had to be replaced.
so the story here is the rear cam sensors start leaking internally and that oil travels inside the loom. how common? VERY. any Subaru with these rear cam sensors are prone to fail and leak internally. the most common one is the Impreza and Forrester, since these models have metal casing they get loose and oil travels inside to the loom. FIX. if in budget and no codes are thrown, simply pull out the sensors, thoroughly clean metal casing and make sure there is no oil residue. apply three bond sealer around the surface where the metal casing and plastic parts mates. wait for dry and install back. if the oil hasn't penetrated through harness enough than cut the harness plug and join wires using bullet connectors, this will ensure oil falls off (if it decides to leak again) through the connectors before it travels through. if not in budget and you have a deep pocket, than go ahead and replace the sensors.
when the oil travels through the harness, the wires get hard and starts breaking internally. on operating temperature it can cause a lot of performance issues. best way to find this is to unplug the harness and check for any oil residue. if the is than change the harness and use bullet connectors on the cam sensors to prevent oil travel.
ive seen a lot of these and 8 out of 10 of these vehicle had engine blow by. is the blow by cause of this? I cant be 100% sure.