I'm not 100% sure about this, but it looks like Castrol has discontinued the GTX 10W40. It has always been spared the friction modifiers because it was considered "motorcycle oil". The last few times that I have gone looking for it, it's getting harder to find. I suspect with Castrol's motorcycle specific oils coming out they have dropped the GTX 10W40. Chances are it is the same oil under a different label at a higher price now. What am I gonna do? Walmart Super Tech 10W40 seems to be the only replacement for me now.
Scott
Scott