I'll go right back to when I first viewed the car. The car was showing a CEL. He claimed it to be the same sensor. I asked him to go get it fixed and if it comes back with no codes then I'll buy the car, which it did.
With regards to the tune, the old owner claimed to have run it on 95. Right from the word go, I have always religiously run on BP 98. I did a few tanks on BP 98, then had the ECU reset.
Anyway, problem is fixed. New fuel/air ratio sensor has been installed (genuine Subaru part). Comparing the two, I don't think the one that broke was an original part like I was assured ..
My reasons are, the new genuine one I bought had chassis clips to clip the wire to the chassis up to the plug, where the broken one didn't, it was just cable tied with no factory mounting clips. Also, the numbers were different on both sensors. I expected them to be exactly the same. The part numbers were correct, but on the broken one there were different markings and numbers ..
Feeling a bit let down as I'm rather confident the old owner purposely did not pay big bucks for a genuine part, instead tell me otherwise.