A while ago I had picked up a pretty nice 1889 Remington hammer gun. There were some dark water stains on the butt and I used some wood bleach (having oxalic acid) to remove the stains. I brushed it on the stains let it sit a bit then rinsed with clean water. I've done this 5 times, most of the stains have disapeared. It doesn't seem to be removing any more of the stains. Should I keep going with wood bleach or is there something else that would get the last of the stains out?

Thanks,

Jack K