KingD19
Shai-Gen's Enigmatic Wong
Weak spot perhaps. I dunno. I'm not denying it happened, because that'd be silly. Just like saying, "Oh, we only saw internal defenses in this one spot, so he must not have any anywhere else, despite him being bigger than most known planets and only a few parts are shown due to it being a movie with time constraints!!" Especially since when Perceptor and a few other Autobots shrunk to miscroscopic size and went inside Megatron, he had internal defenses as well.
But the fact of the matter is that in pretty much every iteration of comics/movies/cartoons/video games that involve Unicron, the only way to defeat him is the Autobot Matrix of Leadership, or being attacked head on by his brother, Primus, who is actually a transformed Cybertron.
So while he may be able to be damaged, he certainly can't be stopped or destroyed without it. In some continuities he can even heal damage done to him in moments.
And are you stating you don't believe Hot Rod evolving into Rodiums gave him a massive power boost? Despite Optimus' "spirit" telling him to arise and take on the mantle of Prime(which always makes a person strong), him becoming visibly larger and more menacing looking, him being able to easily overpower Galvatron when the weaker form of Megatron was sonning him in the beginning of the movie. And Galvatron hurtling through space uncontrollably for months before a planet's gravity well finally caught him.