I only have my own experiences, I mentioned them previously, but I haven't published anything on it, so I'll leave that aside. Lubehead did make several references to heavy equipment, and that is where much of my experience has come in the past 20 plus years. We (as an industry, not just the manufacturer I work with) have maintenance programs that are generally much more advanced than typical automobile maintenance recommendations. I didn't invent any of them, I just work with them.

A couple of observations, apologies if I am prescribing opinions to you incorrectly. a) You base your maintenance plan on the assumption that the transmission is more likely to fail as it ages. This isn't necessarily true, over the life of the asset. b) You are looking for hard data ,when it doesn't exist. c) You promote a generic maintenance schedule, ie a fixed fluid change interval.

I have attached an article by an organization that teaches how to determine maintenance requirements of a physical asset. It seemed appropriate. Apologies if you have read it and are familiar with it. The three points above are covered in the article. I also think you will really enjoy maxim #14 in the article, which is all about not blindly following the equipment manufacturer's recommendations. Yes, I can see both sides of an issue

Incidentally, the article is 15 years old, ie years before the first X5 was manufactured. This stuff isn't new. Hope some here find it interesting.

Maintenance Management - A New Paradigm

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue