When I first purchased my current RT it had 36,200 miles on the clock. I pulled the valve covers and cylinder heads for inspection. The valve ports were pretty dirty and had built up carbon on them. The piston tops looked about the same with a 3mm carbon ring. A carbon ring around the perimeter of the piston is actually a good thing (if you weren't aware of that).
After flushing all the fluids I ran 2oz of Marvel Mystery Oil per tank and have been doing that over the past 2,700 miles. I did a high-speed trip from Colorado up to Hardin, Montana last week and averaged 78 mph. This helped heat the piston tops over a long period of time to assist in cleaning them.
I pulled the valve covers and heads last night. All of the carbon buildup inside the ports, on the valve faces and on the pistons is now gone but the carbon ring is still there. Couldn't ask for anything more from this great product. To get the interior this clean you would normally have to do a mechanical cleaning such and a chemical soak and glass beading.
Try it and your Beemer will run better and more efficiently than it ever has.
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