History: knocking/loss of power/low on oil, added oil - much improved. Drove 1 mile knock and power loss returned. Suggestions: drop oil look for signs of metal, check for rod bearing (sequential plug removal), compression check, oil pressure check, listen to block via a long screwdriver for location of sounds.

UPDATE: I think it's toasted.

...after this workweek, dropped oil- no signs of metal, tried to do all tests again but will not idle. Knocking is much worse and now intermittant with new rattles, and clanks added to the symphony. All are very metallic sounds. I was going to change out the oil pump and pull the valve covers and cam assemblies... but I think it's a hopeless waste of 6-10 hours and money. I am going to pull the oil pan and check it for metal and see what the underside looks like but I am not hopeful.

Its a shame only 140K on this Subie.

That's too bad. You could take an oil sample to get it analyzed. The local caterpillar dealer here does it for about $10 and it tells you what metals and contaminants are in the oil and what it all means.