Had similar problem after installing a new radiator. So, installed a new cap, then a second new cap. Still smelled antifreeze and could sometimes see small amount of antifreeze at the base of the filler neck. Put a small hose clamp on the hose to the overflow tank. Problem solved. Apparently after 165K miles the flexibility of the hose decreases so that it won't seal.
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Yep, that does happen quite often .. after "installing a new radiator" and that hose is removed and re-installed.