Walter, I'm interested in your current perspective on the suitability of the BMW for a trip like this. As a mechanical engineer I fully understand the concepts of 'design life'and 'fit for purpose'. Your bike has done well but in all fairness, this is the type of riding it's supposed to have been designed for. Cracking brackets (especially aftermarket) I can understand, but bolts loosening and going missing rings extreme alarm bells. This is usually an indication that the material that holds these bolts is undergoing stresses beyond it's original design criteria (and not just the bike getting too old for the job).
This is not a brand bashing post (I owned a BMW for a very satisfactory 6 years as well) but considering your first trip on the Honda 400 twin, which was relatively trouble free, I can't help to think that the consumer driven weight reduction in heavy off-road capable machines, coupled with a stagnation in engineering fundamentals, has created a class of bikes which are a little too weak to 'get flogged to hell and back' and keep on riding.
What I'm really trying to say is; twenty years ago you could take a stock machine, put a set of bags and some crash bars on it, and literally ride the world. Even though the technology in modern bikes is awesome, how much prep do we need to consider on the current crop of machines?
'Work is the curse of the drinking classes.'