Honestly, I've made a coupe of hundred cakes in the past couple of years and this has never happened to me!!

yes...I did "butter" the layers and make a dam before the jam. But, it is oozing anyway! The only thing I did differently is that I didn't freeze the cake before leveling and icing.

How can I salvage this?

I know you said you used a dam but it sounds like your frosting wasn't stiff enough. When I make my butter cream I initially add less water so that I have a nice stiff frosting to dam my cakes. Once I add the filling I add additional liquid until I get the desired consistency. After adding the top layer I gently press down the cake and remove the excess frosting. I let the cake settle for a hour or two with a plate or tile on top to make sure the cake has settled and no filling bulges appear. Hope this helps.