Can I use new cedar semi transparent stain and sealer to cover natural Australian timber oil

Thanks for taking the time to ask a question. No, in order to be effective, the stain must be able to penetrate into the wood. It's best to remove all previous coatings. Prepare previously stained or weathered surfaces with Cabot® Problem-Solver® Wood Cleaner, Wood Brightener or Wood Strippers. I hope that helps. Respectfully, Reggie