Question... as the API Seal/License on prospective engine oil manufactures labels is voluntary, what makes brand X with API Seal/License better then brand Y which doesn't have the API Seal/License and is exactly the same oil?
You see, API seals are, from American Petroleum Institute website:
API’s Engine Oil Licensing and Certification System (EOLCS) is a voluntary licensing and certification program that authorizes engine oil marketers who meet specified requirements to use the API Engine Oil Quality Marks
as you might have guessed, an engine oil manufacture has to pay for the API Seal/License and its not cheap, as well has to yearly to maintain that API Seal/License .
Amsoil was the first 1972 "API rated" synthetic engine oil produced and sold. They don't carry the API Seal because the refuse to pay the "Ransom", API charges for their License fee.