[Merc6]

After a real long drive on a straight away, like 15 hours, my arms tend to get stiff. Not doing anything, just hanging unto the steering wheel.

Should I see my GM dealer about this?

Yeah you could, not sure what they would do besides take a long Dora the explorer pause. You might get the guy who semi takes it serious and tells you to extend the arm rest, telescope the wheel as close to you as you can and get you a little bit closer/higher seating position.