correct gas cap for 86 V45

[Magna86]

Awhile back I posted a topic about my gas cap seeping gas after fillup. I have not been able to fix it yet. But someone told me my tank may have a slight amount of damage or out of roundness that can't be seen by the eye. So I purchased a good tank from a running bike(85 v45) on ebay. When the tank arrived I was going to swap caps but this one was drilled out and would open with a screwdriver but bit very effectively. But when I looked at the cap it was different than mine. Mine has the vent tube with the black plastic screen cap on bottom. (which was new in box when I bought bike) The 85 is just flat with not vent tube. Just the round part with the locking tabs. Which one is right and could that solve my problem? Post pics of the caps on you 85 and 86 tanks. If it would fix the problem where can I find a new one of those? Thanks