One of our members reparing them professionally. He knows every nut and bolt and can fix them really well. I don't remember his nickname, but I'm sure he will be in touch with you when he see your post.
It sounds like the second section might be too well-attached to its seal to lift off and slide back. Does it go if you give it a little help lifting from inside while holding the switch?
Agree with @Proghound, a helping hand on the second panel, pushing upwards whilst opening the OSS might help. Tricky to do with the sunblind on though. In case this works I'd strongly advice to clean and apply the correct lube on all the seals, to prevent sticking in the future.
Gummi Pflege is the most effective cleaning/ nourishing product for the rubber seals and Audi OEM lube is G-000-450-02.