98 350 Radiator Overflow Bottle

[bomber]

I'm chasing a odd leak, my overflow bottle seems to leak around the plastc cap. It's not overflowing and it's vent tube is quite open. I figured I'd change the radiator cap first to see if it still happens. if not I'll have to get a new overflow cap or perhaps some gasket material to seal it back up.

 

Is this odd? has anyone had the cap on their overflow bottle leak.

 

Also I was wondering why replacement radiator caps are rated for 16lbs? The origional OEM is 15lbs. Any suggestions on what one to replace it with? I'm thinking it could be part of my troubles, and if not, well it couldn't hurt.