I thought you couldn't get the health regeneration until further on. Or is that the resurrection one I'm thinking of?
Anyhoo, I used the shield, lightening gun (go around the outside of the facility and approach the hanger from where the plane is to get it before triggering Starscream). I also use grenades and armour. Keep firing the blaster at SS, even when he transforms because he stays in one spot when he does and you can get some cheap shots in
. When he strafes you, run sideways and unleash the gun and all the grenades at him. You'll eventually wear him down. When he comes at you with his (unblockable and painful) sword, I find the best thing to do is to transform and drive away quickly. Eventually, he'll get bored and transform back to jet mode.
P.S. IMO Starscream has the best transformation of the game. He's the only one with an in game transformation who actually looks like he's transforming instead of 'flipping' (for lack of a better wod)from one mode to the other.