If the cap is leaking, remove and clean the gasket, reinstall the cap and I  
use a specific tightening pattern. I start at the center on both sides and 
work  my way back and forth to each end. Do not tighten fully in just one pass. 
Take a  little each time. It might take three or four attempts to tighten, but 
this way  you will apply even pressure over the full length of the cap. 
 
Rummy