On Friday, May 25, 2018 at 11:23:52 AM UTC-4, wrote:
This happened on my ASW-15 a few years back - when it was stored in the locked trailer in a garage over the winter. It was fine on the last flight of the year at the end of October and when I took it in for the annual in spring I noticed the ASI was off when I looked in the cockpit. The diaphragm had burst at the edge sometime during the off season. I think in my case it was just age.

It is quite common that moisture builds up in the diaphragm and causes corrosion at the bottom edge, eventually leading to failure.
I've seen it a dozen times.
Any glider kept outside that has had a pitot blocked by water needs to be drained and dried. Obvious, but people don't do it.
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