Take the ends off the 'cannisters' that leak and check to see if there's a rubber seal/washer type thing at the bottom of the thread...
Mine doesn't leak and i tighten it by hand, only time it did was when I forgot to out the seals back on!
Are you priducing into an ibc tank/storage tank?
If so, change the membranes (the ones that sit on top) to 150gpd membranes. Add a third, and then you'll have a 450gpd
Dont see the point for having any less than 450gpd, for the amount membranes cost it'll save you having to leave your R.O on allllllllllll the time...