I'm not familiar SeaTech but they look like compression fittings. Maybe you assembled them incorrectly?

With Pex fittings, you can use compression fittings as well as a clamping collar system. The compression fittings work fine if you install them as designed. I've not had too many problems with them but I'm not as confident in compression fittings as the press on type. And the compression fittings are much more expensive and take up more space.

With the clamps, you use a crimp tool that presses a metal collar around the Pex which is over a metal barb fitting. You have a tool that can then be slid over the joint to check it. If it doesn't fit, the joint isn't correct. It's fool proof. (sorry)

I use the rachet type of crimper. I'd have a tough time using that in the nooks and crannys I have run tubing on my boat. But if you have the space, they're great. Pex will require more space if you want to bend it. About a 6" radius is the best it will do without crimping. Meaning, if you have to turn 180 degrees, you'll need a foot of space or you'll have to install 2 90 degree elbows.

With h/c reinforced tubing, I find if you use the more expensive metal barb fittings, quality correctly sized hose clamps, leaks are rare. But it is more expensive.