As for using wheat flour to seal barrels, yes, this is still done by some barrel makers, but all barrels, especially new ones, are steam power sprayed to remove any and all contamination, as the last thing a wine maker wants is something that would contaminate his product. I have seen this high-pressure steam power washing personally, and it is basically to sterilize the inside of the barrels.
I live in Sonoma County and have visited dozens of wineries here, and have spoken to each about this, and none of them believe you would ever find any detectable gluten in their wines from the way the barrels are made--basically if it could leach from the sealed area the barrels would leak, and they don't (or if they do they are thrown away). Even if there were minute amounts of gluten due to leaching, the wines age for at least a year and are left undisturbed. All particles settle to the bottom of the barrel, and the wine makers take great care not to disturb the sediments when they pump out the wine for bottling--the bottom settlements are never used, which is where the clearing agents and all sediments end up.
I believe that when you present such information you need to back it up with something better than a post to some very old rumors that have never been substantiated in any way, like through testing. I have considered offering a monetary reward for anyone who can show me a traditional red or white wine that tests positive for gluten...just to settle this issue once and for all.
Did I mention that my co-worker's husband here at Celiac.com owns a wine label and has been making wine for 20+ years? I've talked to him about this and he agrees that gluten is not something you need to worry about when drinking wine...