If you have towed the vehicle up and down several elevations changes I believe you have no issues.
And the story goes like this - I towed my 2002 K1200LT from Cincinnati to the CCR in
Breckenridge, CO. While I was gassing up in Dillon I noticed oil from the rear drive all
over the wheel. And there was no explanation why since the rear wheel did not turn
for over 1500 miles and it just sat there on the trailer. When I got the CCR I
approached the BMW service guys from the Denver dealer and they said not to worry
happens all the time in the mountains when trailering BMW's. Just top up your rear
drive fluids and away you go. It appears that near the top of the vent hole there is an
area where oil can get trapped and when you change elevations this oil can get
sucked out by normal atmospheric pressure differentials.
For the record the following elevations apply:
480 feet above seal level
Is the highest vehicular tunnel in the world, located at an elevation of 11,013 feet
above seal level
9,800 feet above sea level
BTW, when I trailered home there was no leakage ???