Mine are the same DJ. I always used a blow off for fermentation as I fill my brew buckets pretty full but I tried the Sterilock on a 16L batch recently and found it built a lot of pressure in the fermentor. They're fine for cold crashing and conditioning but I'll stick to a blow off or 2 piece airlock for fermenting and use one of my WW's if I want to ferment under pressure.
Herr Bribie, I'd measure the height of your clips and see if they're all even. If one or two aren't try putting a bend in them to help them pull down more.