If it is the quick connect that is leaking, there are 4 possible sources for the leak:
The 2 ends where the hoses connect to the device - sometimes the hoses work themselves out of the threaded "grabber". If the hoses are quite stretched out, you might need to trim the hose a bit to get at a "clean" edge that the grabber can grab on.
If it is leaking from the middle, then it is probable an o-ring that is gone. Open the quick connect & pull out the middle sticking out part. <It is a short tube, normally only only one end comes off when you disconnect, but that tube comes out separately.> There should be an o-ring on each end of that tube. Chances are, one of them is bad. <I use standard o-rings of the same size/thickness from a plumbing supply store ... must less than the Marineland ones.>
If you have to replace one, you may as well replace all 4, both the in & out part. The "out" part leaks because it is under pressure. The "in" part won't leak, but will suck air in to give you cavitation problems.
I also had the little tabs breaking off in the quick connect, making for a loose fit. I had to get rid of one set because of this, & replace it with jsut a lenght of hose.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.