Stick with your closed system.
Either buy the aluminum bottle, or try another plastic one. Make sure you get it from the dealer, or from a guy named
Gerr on here.
I just got one from Gerr, and it has been the best thing i have done so far. The cap always stays tight, and i have no problems with it at all. Definetly better then any of the many replacements i have gotten. For the price, you cant beat it.
As i have said all over this board however, if this one doesnt do it for me, im going to get the Aluminum one... Use the search, youll find some threads about the aluminum tank from macs.
Also, make sure the cap isnt hitting your hood when you close it.