This thread has confirmed what I have found out by mixing and trying all kinds of flavors: butterscotch, like coffee, just seems to be one of those flavors that are very elusive.
Fruit flavors seem to be the easiest.
I thought it was my lack of skills, but we have all kinds of new B&M's here in Grand Rapids including Mr. E Liquid which is very popular on ECF and has a good reputation. We also have another store with a nationwide following.
Their coffee and butterscotch are no better than anything else I have tried, DIY or otherwise.