This is not so much a question as a series of observations, encounters, troubleshooting, and different attempts at stopping all the damn water all over the place...
Well, not too bad, just lost about 3 gallons.
I did my monthly filter cleanup over the weekend, specifially on Sunday and when I woke up Monday, I noticed my 29 gallon was down about an inch. Holy ####. Upon inspection of the XP2 I first thought the water was coming from between the canister and the motor top. I took it off, rotated it around, and reseated. Still leaked. Damn!!. I ordered an o ring kit (haven't cancelled, just want them on hand).
I have a spare XP1 so I swapped the two filters out, topped the tank off, watched it for about 5 minutes (no leaks) and went to work. I come home and the water is about 1/2 inch below where it was in the morning. Double damn. I have a real close look and see the real (turns out usual) suspect: coming out the power cord hole of the XP1. So, it isn't something with the main body of the XP2 filter itself. I switch back to the XP2. I didn't have to do what I did next, but I took the motor cover of the XP2 off. It doesn't reveal much save the top of the actual motor which is sealed and the cord. So I put it back together.
Next, I look at the quick disconnect itself. What was going on should have tipped me off, but I'm too new to filstars still. It had been dripping, so I had it in a bucket to catch the water. I tried changing the o-rings. No dice. Still leaked when I put it back together. Triple damn.
My last resort: I took the whole disconnect assembly from the one that came with the spare XP1 and swapped it out with the old quick disconnect. To do this, I had to cut it off. Now, I thought by raising the hoses the water would drain back in, but when I cut off one hose, it started to siphon anyway and went all over an easy chair. Oh well, I never sit in the thing anyway. Like an idiot I hadn't brought the bucket with me. I wedged the hose where it would not be likely to come off and got the bucket, which wasn't too far off. It did un-wedge itself and really soaked the same chair again. I definately will not sit in it now. I cut the rest of the old disconnect off and raised the other tube up to drain back into the tank so it would not siphon. Thiis was the inlet hose. When I did that it came off the heater. Minor problem, fixit later.
All that was left was to reconnect the spare disconnect and everything else. I used my keg lube from my homebrewing and yet it still was a bear to reconnect the hoses.. (I do recommend getting a food grade lube, like keg lube: makes putting these hoses on easier.) I think the difficulty was the tubes were a tad grungy.
The rest was routine. Clamped the hoses on the inlet outlet tubes, re-inserted into the motor head, reconnected the smart heater and turned it back on. VOILA!!! NO LEAK!!!
I topped the tank off.
For whatever reason, I decided to test the water temp with my finger and my oscar bit me. Now that's gratitude for you. At least he didn't end up on the floor like the last time. Next time, I'll use my thermometer.
Moral of the story: there really isn't one, save this perhaps: make sure where the leak is coming from.
two cents ¢¢