Understood, my point was things can change, allegiances change. My G1 knowledge is a little hazy, but unless I'm mistaken, Magnus' past isn't revealed in any of the shows. Although I personally don't believe he was once a Decepticon, I just think that it's possible.
I'm with you. I like the idea that despite their age Cybertronians are capable of chaning their minds as the centuries roll on. They are sentient afterall, and so they may be programed (for lack of a better word) with a function (like how Ratchet is a medic) but not necessarily programmed to follow any particular set of unchanging, linear allegiance. I think a sort of appropriate G1 example would be Mirage or Thundercracker, who are both to varying degrees not at home with their faction ideology. They are fairly middle of the road kind of guys though; I strongly doubt you'd ever see the real wild, bloodthirsty Decepticons going over, or some one like Beachcomber going to the Decepticon side.