Hello!
We're talking several subjects here... Hasegawa decals - they can be so mean! One friend of mine once said the trich to those decals is to put some MicroSol on them, and then to take this MicroSol right away with a clean tissue paper - and then the decals supposedly work all right. If you let the MicroSol stay on the decals as you would with any other brand, the decal will most probably go bad (for example wrinkle and stay this way).
Now chipping - sometimes it's funny to see a model weathered almost beyond decency but with insignia all in one piece. It would seem obvious, that those should also get scratched, chipped and so on. If the layer of paint the insignia were painted on should chip, the chips on the insignia would be down to primer or even bare metal, right?
In a pinch such chipping could be done with a sponge - just go easy with it, it would also be unreasonable to expect the chipping to concentrate on the insignia.
Once I 've done this:
The front star is based on historical photos of the vehicle and it looks like the other stars were repianted and this one not - because it made too good a target for the Vietnamese gunners. I did the chipping by cutting a star out of masking tape and applying white with a sponge through a mask like that.
That might be a solution for you, too - remove the worst part of the decal and try to partially repaint it with a correctlyshaded paint - this sometimes works very well.
Anyhow - good luck with your project and I would love to see some photos! Have a nice day
Paweł