Any of the above.
If I suspected sludge, I'd try to remove a valve cover to verify it.
Sludge is usually the product of oil run too long, allowing oxidation to overwhelm detergency, or a bad PCV system or both.
Any oil changed on short intervals will gradually clean up the engine, from what I have seen.
I'd lay in a stock of some FAR oils, like Nextgen and G-Oil, as well as some decent filters bought cheap after discount, like P1s, and plan some 2-3K oil changes.
I'd try to avoid short trips with the car.
After a few short runs, which should greatly reduce the amount of sludge, and assuming that the oil pickup screen is clear (easily verified in some installations, but there are others where removing the oil pan is a major project), I'd maybe try a short run with Kreen, which should clean out everything that remains.
I might also price out an exchange or used engine, in case the patient dies during treatment.