Be careful letting the membrane sit very long in a high pH wash. Most membrane manufacturers would recommend against it... one or two hours maximum. High pH will eventually destroy the membrane. The membrane is probably fine. Bacterial growth is making it stink. Once you've removed as much of the odor as you can doing soap washes. You probably can just store it in the sodium bisulfite solution over the summer and it will be fine. This is a antibacterial material used for sanitizing wine making equipment and it should kill any remaining bacteria in the membrane. Make sure you soap wash it a couple of times before you use it next season.
Leader 1/2 pint - Kawasaki Mule - Smoky Lake Filter Bottler
24 GPH RO, 2 1/2 x 40 NF3 (NF270), 140 GPH (Brass with no relief valve ) ProCon pump
2013 - 44 taps - 16 gallons syrup, 2014 - 109 taps - 26 gallons syrup
2015 - 71 taps - 13.5 gallons syrup, 2016 - 125 taps - 24.25 gallons syrup
2017 - 129 taps - 17.5 gallons syrup, 2018 - 128 taps- 18 gallons syrup
2019 -130 taps - 18.5 gallons syrup, 2020 ~125 taps-19.75 gallons syrup