I replaced the original heater core and o-rings with a Nissens in my 1995 850 turbo less than a year ago in 4/2010. The other day something inside or near the heater core sprung a major anti-freeze leak to the point that there was nothing left in the reservoir tank and very little in the radiator when I opened the drain plug.

Is it possible that the new heater core is faulty? There was a lot of anti-freeze in the blades or is it more likely that the o-ring failed and the anti-freeze was sprayed into the blades?

It did not seem like there was a gallon worth of anti-freeze/water in the cabin under the carpet and if it all didn't go into the cabin where did it go. I didn't notice any outside of the cabin but it was dark so I couldn't tell if there was a puddle under the car or not. It didn't seem like there was.