If there are any problems, just stay calm.
It took me the whole day to get my bike out in LA.
They wanted to have some official documents from BMW (which I of course did not have), so I told them I will go and ask these.
Later I came back and told them that I called BMW NA and they said I do not need that paper.
Answer was "ok, but do you have this another paper (which they do not need)?".
I told them, no, I do not have it, but I will make some calls and ask if I can get it. An hour later, I went back and told that this paper is not needed either based on BMW NA answer.
On my fourth visit all original papers were enough and I was able to get my bike...
I had to bite my tongue few times, but stayed calm, because I knew if I start arguing, they might say "sorry, your paperwork is not in order, so cannot bring your bike over here"...
Landborder between Canada-Alaska (US) and Canada-US went without a single paper, just showed my passport and they asked where I am going. Once I told them, they said "do not go to Mexico with your bike, because you will be killed and they will take your bike..."
Well, still alive, now in Guadalajara