11,000 miles on my 2012 trophy and no cracks... as others have mentioned, the issue is overwhelmingly specific to US models where ~10% ethanol is the usual in the fuel, but also where the charcoal canister is fitted.
As the EU has approved up to 10% ethanol in fuel recently it will be interesting to see if the problem migrates this way. Fortunately the fuel stations are obligated to clearly mark fuels with ethanol and the majority will either have no ethanol, or have ~5% ethanol on super plus grade (≥98 RON) so it will be easy enough to avoid this.
What's interesting is that BMW have confirmed that all of their bikes are approved to run on up to 10% ethanol.
With this in mind, and on the assumption that the ethanol content isn't causing the problem (go with me for a minute)... are there any special/unique requirements for the packing/shipping of the bikes in transit to the US which may be causing damage to the tanks on a good number of units - something different from bikes shipped to other countries/continents in the world?
BMW Motorrad official technical FAQ translation:
Please refer to the notes in the operating manual of your vehicle or ask your BMW Motorrad dealer.
BMW Motorrad riders can soak E10
For BMW motorcyclists results from the introduction of E10 fuel no change. In all model years of the BMW motorcycle models all use is harmless.
Since January 2011, there are at gas stations, a new type of petrol with the code E10. Under E10 refers to gasoline with up to ten percent bioethanol. With the introduction of the new fuel Germany is implementing a regulation of the European Union, which wants to reduce CO2 emissions and to protecting the climate.
All vehicles of the current BMW Motorrad program, all older models can easily be operated with gasoline, which have up to a ten percent ethanol content (E10). Please note that the recommended or prescribed in the relevant operating manual fuel (eg premium gasoline with 95 RON or Super Plus 98 ROZ) are complied with.
Fuels can painted surfaces and plastic parts affect and damage. We therefore recommend that when refueling proceed very carefully and to prevent splashing of fuel possible. Remove spilled fuel residues immediately and thoroughly as possible. This is especially true for windshields, the cockpit, the motorcycle luggage system, but also for the rider equipment.
In classic motorcycles with carburetors, we have the experience that can corrode after long periods of, for example, over the winter, the float chambers, floats and float needles. This is due to the hygroscopic properties of the proportions of alcohol in the fuel, which bind during long periods of water. Reduced extent this also applies to the currently available fuel with five percent ethanol content (E5). Age, water retention with contaminated fuel in the float chambers can also cause the bike poorly or not start after a longer service life. We therefore recommend especially for the storage of classic cars motorcycles to remove the fuel from the carburetors.