Fuel filter, Oilhead
Changing the fuel filter in my R1100RS was a major pain.
A whole lot of taking shit apart to do a simple maintenance item.
And while I'm bitching, bleeding the ABS brake unit on the same bike was an exercise resulting in moderate brain damage.
Valve check on Superhawk also a knuckle smashing , teethgnashing procedure. Swapping a Fox shock in to the VTR also damaging to fingers.
I'm sure there are others, like trying to stop Triumph Bonneville push rod tubes from leaking ...or ....nevermind.
But my GL1000 air filter was no biggie, but it's hard to remember if I actually ever changed it.
The most aggravating things are often the ones you would think should be easy for anyone to do. That must be why mechanics have job security.