There are two methods for doing MM, and your post has confused me about which hand goes in the pocket in the roof. I'm pretty sure I did it with my left, this being a hard move that stumpies find especially difficult. Thereafter the swing felt okay to me; the mantel did cause a further wobble, but not as hard as the start.
The stumpy method takes the roof pocket with right hand, then a sloper at the lip, and I can't remember the rest, although I have seen Crooky do it this way.
MM is great, but in retrospect, Bombshell is the better problem.
I hope that cheating stone in the break has not been moved back!