Slow Cooker makes a mess I tried googling this one but I just kept getting recipes. 

I bought a slow cooker (Proctor-Silex 33043 4-Quart Slow Cooker), which seemed to have good reviews. However I try to make stock, which I would normally cook for 12+ hours, every time that I do it bubbles over. It isn't to say that the liquid itself boils up and out of the pot but rather a ring of liquid forms on the edge of the pot and begins to bubble outwards.

It causes a mess by burning inside of the metal part of the pan (in-between the heating element and the stoneware part) and spilling down the outside walls of the slow cooker onto the counter.

What can I do about this? Is it just a bad slow cooker or is there a trick I'm missing. I haven't encountered this problem before with my old cooker or pot on the stove. I was considering inserting a toothpick in the edge or something.

Has anyone else encountered this? Is it because I'm making very liquid stock vs say a heavier dish like oatmeal? I've tried shallow (less liquid) and very full but it occurs in both scenarios.
The solution is real easy and you won't need do any of the crazy stuff mentioned above. Buy some baking paper (brown (sort of waxed) paper that you can line baking trays. The often come ready cut in baking tray sizes, which are plenty big enough. Fine the area that will be in the center of our crock pot when the lid is on. Take a sharp knife and cut an X shape in the center. Have someone, although, it can be done alone, gently pull the paper taut, not tight, and put the lid on your crock pot (with the X in the center) and gently press it down. You'll feel the paper seal the lid to the pot much better. Then as the steam rises through the paper it will condense on the lip and drip down onto the paper and will be funneled back into the pot by the X you cut in the center of the paper. Your problem will solved, for the price of baking paper. Best of luck and best of slow cooking without the mess.