This one turned out very well, in my opinion. Not a sound stamp, but infinitely more attractive now. I bought it on eBay specifically for a soaking attempt, thinking that I might be able to improve it.
Warm to hot water, a few drops of dish soap, about 3 minutes using tongs to “pull” the stamp through the water, then a rinse in clean water, and then 3 days in a Desert Magic drying book with about 30 pounds of weight on it to press out the stamp.
Seller’s before picture (Ickypoo!):