Hi ,
I too have KF5 with 912uls.
I currently am using Aeroshell Sport Plus4, it is semisynthetic. I notice a very slight oil coating on belly from breather line . I think I might have filled the oil tank a little high at last oil change.( right at full mark on dipstick)
The oil level on the dip stick has seemed to stabilize in the middle of the two marks now, checked after burping.
I think you have just a little too much oil in your tank, when it heats up and expands some is going out the breather. Blue Skies!