Originally Posted by GAS GUY
You can run 75w90 or 80w90 or the 140 weight in syn or dino.
Just make sure it is a good quality oil with gl5 rating.
The most important thing is to make sure not to overfill your FD.
+1 on the above, with one comment. When I lived in Wyoming where it was much cooler, I ran lighter gear oil (same in both tranny and FD) than I do in Virginia. I've run full synthetic for years and never had any issues on three different BMWs so far. I've had two crown seal failures, but both were on bikes with 45K to 50K miles, just wear items. I changed my GS crown seal recently and did a photodoc on it in case you're interested:
The comment - I'm not sure how you overfill the FD unit. IIRC, the manual says fill to the bottom of the threads and that's just about as much as you can get in there without it drooling out. If you were somehow able to overfill it, it's vented and would likely just blow out, right?
Don't overthink this, it's the easiest service you can do on your BMW. I change my gear oils every other oil change, and do oil changes (also full synthetic) about every 5000 to 6000 miles.
Since you're new to the BMW service world, here are a couple more links to things that might be of interest. I've wrenched for decades on my bikes, but I admit to being rather intimidated by the thought of tearing into the BMWs. As it turns out, they are really rather easy to service compared to some other bikes I've had, and you can save BIG money doing it yourself, especially swapping tires:
Check your brake lines!!!
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