Water Rings on Oak

Easy way to remove water rings. Cover with dry dishtowel and iron the towel in 10 second intervals. The ring is really trapped water, and the heat will cause it to evaporate. Naturally, you need to take care not to over heat the spot. Start slowly.

Check out my article on removing white rings:
http://raidz.net/blog/how-remove-wh ... rings-and-water-spots-your-furniture

This is quoted from Mary Hart of Everyday Cheapskate:

"I had a similar problem, and tried for at least 15 years to get rid of it. Nothing worked, including mayonnaise and several other homespun ideas. Then a painter who specializes in antique restorations suggested that I try JASCO Furniture White Ring Remover (about $5). I followed the printed instructions, and it took about 5 minutes to rub it out. That ugly white spot simply disappeared. It didn't harm the finish in any way and remains completely undetectable. What an amazing product. Check your local hardware store, or find JASCO Furniture White Ring Remover online. As of this writing, it is on sale at www.paintplus.com for $3.75 plus shipping and handling."

I would think you should get some very fine sandpaper, sand the spot down to the wood, and get some stain that matches and restain it - it should be gone then....worth a try maybe? Sorry I can't be for sure - I just think I have read this somewhere.