I've recently tried to put back into use a Hydor Prime 30 which was in storage for about 4 years.
I replaced the O ring seal which goes around the pump assembly and it is very well sealed now, this is not the issue.

For some reason, when I start using it, and pressure builds up, it slowly starts to leak from the area where the blue clips are (the clips which lock the pump assembly into the canister.

Nothing seems broken or bent or in any way out of shape. The previous owner tells me he recalls it used to do this on occasion, but he can't recall what was the fix for it.

Anyone had this experience, and knows what am I doing wrong or has a remedy?

Thank you!