Mine is the same, I looked into fixing it but to get behind it I think you would have to remove the toilet etc. In the end I glued a magnet to the side of the fridge lid. Something like this:
It isn't strong enough to hold it magnetically but it provides enough of a lip to catch on the springy bit. So basically any small bit of metal would do.
I think it’s a rare flaw in Westy design. I agree it’s not fixable without getting at it from the other side, which is a huge job. A ‘prop’ might work. I used to hold the lid up with my forehead!