USA 239 Plate Drip Fault?

I once brought this stamp into a show to ask a dealer if this was an error or a fault. Essentially, they said that the mark covering the United, "I" and the 2 is a stamp fault that decreases the value. I thought that was unfortunate. Any ideas what could actually cause this fault, and how it affects the value of the stamp? (Of course, the brown mark at the bottom doesn't help either.) Thanks.

Possibly the result of some type of solvent exposure. could be an over inked printing plate issue but I'm no expert on E.F.O.'s. I'm quite sure that someone may point you in the right direction though. Still it's cool looking but that dealer is most probably correct as most collectors want pristine condition. Thanks for posting it though I enjoy the seeing such things.