Look in the stickies in this oil forum above and you’ll get many opinions, then pick one. https://www.hdforums.com/forum/oil-a...ur-choice.html

Can we use an ordinary auto oil? Quite possibly! Is it a suitable alternative to Formula +? I doubt it. There are bound to be suitable alternatives and this forum is stuffed full of threads on the subject, just be wary of the 'wisdom' that gets put around in here. In some ways it is much easier to call by your local H-D dealer and avoid hours of 'research' around HDF or the internet! That's what I do for my Sporty and Buell - my Glide is far from stock and I use oils recommended by S&S and Baker.

There are recognisable industry standards for oil specifications and it would be helpful if H-D told us those for their recommended oils, but unfortunately they don't. The only clue is to use a diesel engine oil as an alternative if we get stuck.