It's not possible for engine oil to get into the transmission unless you pour some in there.
From an intro post of mine:
ENGINE OIL CONSUMPTION: It is normal for K bikes to consume or "burn" oil. Therefore it is a good idea to frequently check the oil level in the oil sight glass window on the lower right side of the engine on the oil sump. (See attached diagram.) The top of the circle in the oil sight window is the maximum oil level while the bottom of the circle is the minimum level.
The rate of oil consumption seems to vary by individual bike but in my experience generally tends to be about a quart every 1500 to two thousand miles. The maximum oil consumption rate specified in the BMW service manual is 0.15 liters per 100 km (2.57 quarts per 1,000 miles) which seems insanely high to me.