This sounds similar to the degredation of the foam core of certain types of propeller blades, when engine oil from the prop hub seeped into the area between the metal spar and the core...caused the loss of at least one Brasilia and a couple of the ATR's in our fleet were found to have weakened blades as well.
I guess petroleum products and glassfibre/composites really don't mix well after curing!
TT