I've said it before somewhere on this forum, but try under filling your final drive by several fl. oz.
This was a HUGE issue on the old R1200c line, and that community also came to the same solution. Because this is a non-ventilated gear system, it will heat the trapped air, and if there's not enough empty volume for the air to heat/cool, it will find a way to exit the housing. What this means is your output shaft seal, being made of rubber, will be the first to go, hence the oil slinging problem.
Let it go long enough and our final drives will likely experience the same catastrophic failures the R1200c final drives did.
Mike