I have a FS94R string trimmer I am thinking about getting a steel shaft from a FS90R for it. If the price is right I might buy one and try it. I think the FS94R is the perfect balance of power and weight but only comes with a cable shaft.
Where can I get Stihl parts besides the Stihl dealer? I am also curious if there is a parts schematic for Stihl equipment? I have done searches and found nothing.
I doubt they have any issues with breaking but that wasn't the point anyway. You apparently are not the kind of person who likes to modify or experiment with projects though so you wont understand.