I think you will find that most of the discussion concerning oil percentages vary wildly. Your engine is a plain bearing engine so most consider more oil better for it in the long run. Another view is that the newer synthetic oils give better protection, another matter of strong debate. If you do get some castor be it from Sig or Wally mart it is just a good idea to add some to your fuel to bring up the lube "just in cast". And the supermarket castor is good stuff as long as you read the label and make certain it says no added sugar or other ingredients.