I've found that the reason is usually because the "coffee tank filter screen" is sitting crooked in its placement and causes the valve to be propped open. But with boiling hot coffee in the tank, it's hard to fix. Sometimes we can tap it with a butter knife and it will sit back into place, and sometimes we've drained all the coffee into a pitcher, waited for the plastic parts to cool, repositioned the filter, and put the coffee back in and turned the pot back on. Depends on how far the valve is propped open and how quickly the coffee is coming out. Hope that helps! :)

I just got the heavy dripping problem started this problem. This happened after my wife made the coffee and switched from brown filters to while filters which (as expected) ripped apart when she tried to dispose of it and spilled into the machine.
Here is the solution that worked for me:
Hold the coffee reservoir upside run warm water through the hole which coffee gets dispensed through. While doing this push and pull the little lever back and forth for about 10-15 seconds. This will clear out the coffee grinds stuck into the seal area and you will get a proper seal gain and leaking will stop. Well at lease this fixed my problem. If you have a loose spring in the same area on the other hand (Which I find surprising based on how much use this spring would get for home use) this will not help you. Good luck.