Thank you for your reply PoolDoc,
Whoever had this house before us - we purchased it in 1997 - drained the pool when the water table was high, and the pool did lift out of the ground about an inch on the west side of the deep end. I've drained it perhaps three times over the past 15 years when it was dry, and it's been stable. About 18 inches of water will seep into the pool when the water table is low. Anyway, I will be careful to wait until we haven't had rain for awhile. There's a creek about 100yds south of the pool which all but runs dry occasionally, and that's when I empty the pool.

So is waiting until the rain subsides, draining the pool, and replacing the valve a reasonable way to proceed at this point? I realize that you would want to be very careful about specifically recommending any particular course of action. Please don't concern yourself over the consequences of anything I might or might do at your suggestion. I'm not going to fault you in any way if things go wrong. I'm sure I've agreed somewhere not to sue anybody over anything that might happen here, and of course that would be my preference, as I want for people to feel free to offer their best advice.

Thanks so much for your help,
Scott