I am currently running Amsoil 75w-90 in the final. Blackstone reported the actual oils weight at 78.5 viscosity at 212 degrees (F). More disturbing is they told me my recent oil sample changed last weekend showed 537 ppm iron where it should only be 142 ppm or less. Sort of disturbing. No play detected .... yet.
I may try a heavier 75w-140 next time if the iron content number is still to high. I will check it in another 7,000 miles per their suggestion to see what the numbers say.
Why BMW cannot get a handle on oil is beyond me. They change their upper oil numbers from 90 to 140 weight as the wind blows and their drives still puke to this day. My dealer now dealer has both 75w-90 and 75w-140 weight BMW branded (made by Spectrol) specified oil sitting on their shelf.
<uh, oh!...feel rant coming on>
I wish they'd get their the hands on their bearing manufacturer and wring their bloody fookin' neck! I suspect mine may be heading south since the chromium level was also high and that is the plating off the balls in the final's race. No excuse for this problem that has been going on for more than a decade now. If they cannot make a decent chromium ball bearing, move on to a more durable ceramic or zirconium ball bearing or something that won't even mind if there is no oil or whatever kind of crap it's lubricated with - even water. Sure it might cost more, but the quality and longevity would be there. But no. Instead they install some cheap-ass looking handlebar controls on the new 1300 and then hike the price. No doubt the same cheap-ass ball bearing resides in that final as well with the apology from that bearing company saying, "Oh, we addressed that problem." Yeah. Right. Prove me wrong after how many design changes, oil spec changes, and lifetime lubricated nonsense.
Hell. The damn yoke bearings on the drive shafts are never lubricated and run 100,000+ miles or more, but the final drive bearings begin to degrade in less than 15K and they are oil bathed! Now really!
Okay. I'm done. I'm going out to rub off some more chromium.