I was just going to suggest that (glad I read the comments first!). "Source Text" is bizarre to people who don't come from an academic background (I don't read TV, I watch it; I don't read music, I listen to it; etc.) "Source Material" is much more intuitive and feels more inclusive.

I know it will mean a boatload of changes, but if we're doing wholesale changes anyway, I think this is the perfect time to make a shift like that.