Sounds like you better check your other HOBs before it's too late! 
I once had an o-ring go bad on a HOB filter and it started to drip water from the seal. I found a suitable replacement at Home Depot, but you had to buy a package of something like 15 or 25 .... way more than 1! Initially annoyed about $5-$7 for the single o-ring I needed, I quickly realized it'd be best to just replace the o-rings on all my HOBs. Money well spent is how I view it now. 
The filter on the 120 was a returned item that had a cracked case. I siliconed the case over the crack and apparently that is not a permanent solution, however it did work for a few months.
The other filter issue was completely due to neglect. I apparently didn't clean it out the past few times doing water changes. The filter basket pushed the top up and it got clogged forcing some of the water over the side.
Neither issue was one of my finer moments.