I have a 2017 FW. At my 1,000 service in CA, the dealer put in HD Syn 3 & on my trip back to St. Louis it felt cooler & shifted better. At 3,750 miles, I changed to Lucas 20W-50 full synthetic high performance motorcycle oil in all 3 holes & the improvement in shifting was immediate. Also, the engine operating temperatures dropped about 20 degrees.
I am glad that I made the switch & I like having the same oil everywhere. I am using the HD 5 micron oil filter. Looking at the specs, it's 1 of the better ones out there IMO.
Here is what confuses me. I don't know if the notion of running the same fluid in all 3 holes just started with the new M8, but the correct procedure for what oil to use where varies from dealer to dealer & even at the same dealership, it depends on who you ask.
I would think that as a company with a new engine out, there would be some consensus on the best procedure, but that's not the case.
1 other oil item of note for new M8 owners. when I had the 1,000 mile service done at the dealer I purchased my FW from, the tech noted it was nearly a quart low on engine oil. He said this is very common in their brief experience with the new engines & mentioned that the MoCo had been getting the same comments. On my 2,000 trip home, the oil was down maybe 4-5 ounces, not enough to worry about, so the oil usage slows/stops after break-in, or at least mine did.
So, what are you all using in all 3 fluid holes & why. Is it cost, availability or both. Also what filter are you using. I wanted a Mobil 1 (used on my cars for years) oil filter for motorcycles, but could not find them locally & after research, stuck with the Harley 5 micron filter from the dealer. They seem to be well made.