This is kind of like standing up in church and asking "what religion is best". Never the less, here goes with my .05 worth. Harley oil is ok, but there are better choices out there that cost about the same. I always go by the "ratings" that all oil is given. API ratings along with different group ratings tell you everything you need to compare one brand or type of oil to another. My personal choice is Mobil 1 V-Twin in 20-50 wt. for the crankcase. For the primary you don't need anything very exotic so I go with Harley Formula + oil. As long as there are no friction modifiers in them, nearly any good 10w30 or 10w40 will be adaquate. For the transmission, well that is a different story. I want a gear oil in there, not just a motor oil. I want a good moly additive in there too because of sheer in between the gears, expecially 1st and 5th which use a straight gear design. I use Mobil 1 Synthetic gear oil of the 75w-90. It has a GL5 rating not a 3 like the Harley synthetic stuff has. You would probably be safe using the Harley 20-50 synthetic 3 stuff in all three holes but as long as something better is available for about the same price I will opt for the added protection afforded by Mobil 1 V-Twin which holds up better in high temp air cooled engines such as Harley. When it came time for my first fluid change the dealer where I bought mine said they now put their Synthetic 3 in the crank, primary and the transmission. Oh, how things change. A couple of years ago Harley wouldn't have used synthetic oil in their motors if their lives depended on it. Now they have their own branded synthetic oil and they have changed their tune somewhat. In keeping with the Harley business model, they will do everything within their power to push Harley branded merchandise whether clothing or chrome. The wise shopper will always shop around and do their homework before buying into that Harley lifestyle that the "Stealers" push so hard. Buy a shop manual from Harley. It will be the best $60.00 you will ever spend with a dealer. Easy to read and it is the very thing the Harley mechanics in the back use.
