Solar vents delivered on Cobra trailers

When I went soaring yesterday, I noticed that the solar vent on my Cobra
trailer was not working. The vent was delivered from Germany already
installed on the trailer about 2-1/2 years ago.

The markings on the vent are "Intersolar" "SOLARVENT" "TYPE 27/28".

After noticing problems with mine, I checked the other new-looking Cobra
trailers in the line with identical vents. Of the 6 others there, vents on
3 were not working.

With this sort of failure rate, I am suspecting that someone on r.a.s. has
looked into either fixing them or repairing them. I live in the U.S., so
any leads on parts suppliers in this country would be appreciated.

Thanks,
Dan