Sanded to 600 grit, that Power Koil 18 coverstock is an oil sponge. All I can suggest is are you sure you thoroughly de-olied the ball?  600 grit with that drilling should be able to handle at least medium-heavy oil.

Maybe some of Do'sc Elixir to prevent oil absorption might help this ball, because it is so dull and because you are using it on heavier oil.

Mine was drilled 5"x4" with pin under the center of the bridge and it hooked plenty with 1000 grit and 1200 grit. In fact, it hooked too much, even on medium-heavy oil; I felt it was almost uncontrollable and I traded it for something else.
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"Just because you can do something does not mean you should do it."