Overheating....

okay, i think that i figuered out my overheating problem that i mentioned in an earlier post. after replacing the radiator cap and thermistat, and bleeding the air out with the little bleeder bolt (thanks to serchef!) and fixing my overflow bottle with epoxy (i love that stuff), im still getting no/intermittant heat from the heater....then tonight i looked at the inside neck of the radiator with the cap off, where the cap gasket sits, and noticed that it looks melted slightly, as the hot gases blow by into the overflow, and now the gasket on the cap doesnt seal it enough. my car runs fine at first, heat and everything for about 15 minutes in stop and go traffic, then no heat, then higher temps on the motor. my radiator fans never came on now they both come on, (but they dont stay on after the ignition is off, arent they supposed to?) HELP! should i replace my radiator? does someone make a good aftermarket one without crappy plastic tanks? should i just try adding some gaskets or using rtv to seal the sucker closed? can i get a cap with a higher opening temp or one that is completely closed all the time!? any suggestions would be greatly appreciated! my baby is going down the crapper!