Dan2.8l

Hello. im new here. so be nice ive had my 2.8 troll for about a year. and a while ago it overheated. pulled over. let it cool. filled her up, went on my way so i could get home n look at it later. now when i pressure test it from the expansion tank, its fine. holds pressure fine, however. when i pressure test it from the radiator. coolant leaks out from the top of the overflow below the expansion tank. is the tank buggerd? yes ive replaced the cap but that didnt work. im thinking the cap isnt sealing on the tank inside properly and leaking pressure? i dont know. should i replace it, ive been quoted $194 from nissan for a new one. and $140 for aftermarket new. so wanna make sure its that before i spend that much on the tank. thanks Daniel.