Run the Castrol. My opinion is that semi is fine, although it is harder to find that now then it was 5 years ago. Now most brands seemed to have phased out the the semi and offer full synthetics only. Gosh, years ago all I ran was petroleum based because that was widely available and never had a problem. I have used Castrol products for over 40 years, that has been my preference but there are many other great oils available.