So, since this Grimlock isn't an Autobot yet but isn't recruited by the Decepticons, he's technically unaligned. Initially I wanted him to just rejoin the Autobots, but what the hey, I think this way would give the guy more opportunities for characterisation.
Just a heads-up, for members of either faction who may want to recruit Grimlock. He thinks the Decepticons will win, but he had served with Autobot members recently... All he needs is a push in the correct direction...