I'm seeing a lot of questions about the o-ring and leaks.
I use a rubber washer between the inside cooler wall and the first SS washer. A second one on the outside wouldn't hurt. The next piece which I think is key. Get some
Teflon packing from your local hardware store. This stuff is used for packing of leaking valves. Cut a piece about 1 1/2" to 2" long, and wrap it around the nipple but inside of the rubber washer. You can stretch and mold it to the length and diameter you need. This will stop the flow of liquid coming out between the nipple pipe and washer. You can put a wrap on the outside as well. The packing will crush into the voids of the coller and washers, and thus stop the leak.
I would suggest trying to limit the twisting of the valve assembly, as I'm sure you have plenty if you have a lot of washers. If the packing is good, the twisting won't matter as long as the rubber and first stainless steel washers aren't turning and are packed well.
Cheers,
Tony