I once owned a 2000 S70 Turbo. It would do the same thing, oil pressure light on and full of oil. I was told that this is caused by bad seals between the oil pan and the block. This causes the oil pump to suck air and get foamy and result in low pressure. I dropped the pan and replaced the seal which is an O ring. No fix.
What I later learned was that the oil passages in the head were so clogged that all the oil was being pumped up to the top of the engine and having a slow return to the sump. This is caused by sludge build up when the is only used for short trips often and not getting up to temperature. The PO of my S70 were seniors who only drove the car on short trips (groceries and church) and most likely never changed the oil. It had 60K on it when I bought it. I replaced the engine with a used one from Erie Vovo but probably could have cleaned it up. Still have it in my garage. I have pictures but never could fugure out how to post them.
You might be able to clean it up by running ATF mixed with oil but I doubt it. Probably have to remove the valve/cam cover and clean it up.
Good luck,
Tom