HA! the forum is amazing! I just started tackling this section marker problem a few hours ago as my first real foray into the world of editing GDL.
In trying to bring our office standard interior elevation marker in as an AC Section Marker element (to take advantage of auto-numbering), I've managed to draw our standard tag, and have the autotext elements work properly. I too have the problem of locating the tag properly along the section marker.
Ideally, as Matthew suggested, there would be interactive hotspots that would allow one to slide the marker along the section. I would also like to be able to have a hotspot at the sheet number tag to move it to a convenient location in a crowded plan.
I've attached a screenshot to show what I'm working on - if any of you have some ideas on how to make this work, I'd be grateful.