I have had both weatherby and brownings where the plastic/epoxy/varathane ??..finish has crackled underneath the outer coat. The only answer is to strip all that finish off. After doing that I ended up giving them a rubbed oil finish in replacement as opposed to trying to 'brush or spray on another hard plastic coating.
I returned one such stock to browning years ago as a warranty issue. They advised that it was caused by the application of a finish coat before previous coats were dry??
anyway, they just replaced the stock with a new one..(that was when Browning was in Montreal!) Personaly I think those stocks are dipped into that finish, so hard to duplicate at home.