What's going on here?

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So I finally got around to pulling my 9920 and checking it out, and the shrink appeared to have been heated up pretty good. Upon pulling it off I found this spot underneath. At first i thought some glue had heated up and melted all over the cap, but now I'm not so sure. Did the cap leak from the backside, or did the FET melt away? Underneath it looks hollowed out a bit...still ran though. Just got hot quick.