Changing intake gasket on a 170, any tips?

I've got this 65 Valiant running pretty good considering it has an intake manifold gasket leak. I put a new gasket on 2 years ago when I got the car but never have driven it on the road but started it a few times. It's leaking now. It's hard to start up. I'm guessing that has something to do with the intake gasket leaking. It idles pretty good, timing is dead on, and idle mixture, and speed is correct. It hesitates at full throttle and pops through the carb. I checked it with a vacuum economy gauge and it's right dead on the line between fair and good vacuum. So is there anything I need to use in order to assure a good seal on the intake gasket? Someone told me to use Copper Spray.