I bought a unfinished oak door at the home store. I lightly sanded the surface and didn’t see any glue on the wood at that time. Once I applied the stain, I had several spots that didn’t take the stain very well. I’m assuming it was glue that soaked into the grain before it was wiped off at the factory. I tried resanding (first pic) one spot with no improvement. Any ideas how to correct this?