I know a few things about Mary Sues I believe..
In Transformers:
Tend to be Seekers and may be female. They tend to have all 'good' traits that make the character ultra sexy/handsome/cool etc,. Doesn't tend to have any negative traits that would detract from this. MS/GS tend to have superpowers, and sometimes can get ridiculously overpowered with them. MS/GS also tend to win nearly EVERY battle they fight, or captivate every male/female they come across.
In Star Wars: MS/GS tend to be Jedi/ Sith. The Transformers description also fits Star Wars fan characters.
But to sum everything up with Tfs and SW, and any other varients of MS/GSs: They basically are TOO perfect. They have no flaws, and are the best in almost everything. They have perfect bodies and cool superpowers. Give your character a mixture of 'good' traits and 'bad' traits, and you will not create a MS/GS.
Addendum: I personally like Seekers as story characters. I don't know why being a Seeker is a part of being a MS/GS, especially a female Seeker, as I don't see a lot of stories about them. If I made up a fancharacter they would be a female Seeker, but she might end up either ugly, boorish, or have some gross nasty habits
In other words, she ain't ever gonna be a Mary Sue.