So my F15 had been through some agricultural roads and needed a pressure clean of the wheel arches. Starting to take the wheels off today, front left to begin with and the headlight level sensor 'regulating rod' is already seized. Now that same thing happened after 14 years on my E53 - but only almost 4 years on the F15.
The front rod was seized at the bottom. The left side rear was starting to seize at the top.
I removed the rods, cleaned and polished the metal, now re-installed.
One to watch as a routine maintenance item, I suggest.