I would not do any additives or flushes in your situation (or any situation really). Flushes and additives just increase the chances of sending larger sized contaminate through the system and causing a more catastrophic issue IMO. Better to slowly clean by using high detergent oil over time or to completely break down the engine and hand clean. Have seen many much worse than that and it did not affect the engine performance; not saying that it eventually won't though, but I don't think it is here from what your are saying. I would check the mechanical items already mentioned, put in a new PCV, then switch to a high detergent oil like one of the Pennzoil products (yelllow bottle for conventional, PP or PPHM for syn) or Valvoline products (Maxlife syn blend, Synpower, or Maxife Synpower) and continue doing your 3k oci's. If I had this car personally, I would button it back up and use PPHM or Maxlife syn blend and run her with a Fram TG until she dies. That car doesn't owe you anything anymore for sure.