I ran a flush oil through my MIL's GM 3800 V6 with ~135k miles. The flush oil is from @High Performance Lubricants and is ester-based with a complete add pack. This flush oil is meant to substitute 1 quart for a normal OCI to slowly clean out the engine. This is the result after ~5k miles. It definitely did its job.
1 quart - HPL SAE 30 EF
3.5 quarts - Havoline HM 5W-30
1 quart - HPL SAE 30 EF
3.5 quarts - Havoline HM 5W-30