2004 R1100S with shifting problem

[goodgravity]

My 2004 R1100S with less than 10,000 miles on it has developed a problem where it will intermittently not shift from 2nd to 3rd gear. When this occurs, downshifting to 1st will usually allow subsequent upshifting to 3rd and higher gears. I have done the following already: (1) checked the shifter linkage (2) bled and refreshed the clutch hydraulic fluid (3) replaced the gear oil with BMW Hypoid 90 and (4) had the clutch spline lubed (expensive). After all of that I am still experiencing the 2nd to 3rd shift problem on a daily basis.

Does anyone have any ideas?

Is it safe to use a transmission detergent in this gearbox?