I hope I don't break the train of thought here. One of my pet hates is the use of two names to discribe the same movement. Get rid of the Grape Vine and call it a Zig Zag. We do one in the Samba from a Promenade then a Zig Zag, Spin into Voltas. Grape Vine never.

I had no idea this was going to be so difficult. (Most of the comments on my question have been so far over my head as to be impenetrable.)

OK, so I S-S to outside partner, so far both steps are identical (I think). Then, if I want to do a quarter turn, my left foot goes forward and slightly left (Q) then my right foot closes (Q) and I am back in closed position ready to go backwards S-S. If going into a grapevine, my left foot goes pretty much left (is this where the difference starts?)Q and my right foot goes slightly back and to the left, behind my right foot Q. So that was my best shot at identifying where the steps depart from one another. But I would still like to get some expert advice (that is relevant to my level and question - I might actually love a "silver twinkle" but I have no idea what one is). Is it that my torso turns to the right LESS for the grapevine than for the quarter turn and that is what I need to point out and/or exagerate for my partner or what? Thank you for the time and attention.

I know nothing about American Smooth. But when you say my right foot goes back slightly to the left behind my RF, If you have your shoulders square to the front it would appear that you are going into CBMP. Is that correct for that step.

What may help with the difference in lead is think of the GV as left foot forward (slow) right foot forward same track (slow) left foot side (q) r/f back (q) left foot side (q) r/f forward (q) left foot side together (qq)

As you finish the second quick there is a slight rise and the lead is from the right hand drawing the follow to come with you.

As for the 1/4 turn or senior walk: left foot forward (slow) right foot forward (slow) same track. then the 1/4 turn on the first quick, the whole frame turns to your right as you step to the side together. (almost like cutting the follow off)

hope fully i did not make things worse...

shawn