Ringland failure is what happens to the piston due to use of rubbish fuel and or lots of high revs on the original subaru map (I believe it ran too lean at the top end in No. 4 pot)
scroll down to Salsas post on the first page for a picture of the piston failure, obviously if not addressed this leads to burnt oil, bore scoring etc
http://uk.subaruownersclub.com/forums/topic/4804-what-fuel-do-you-put-in/