If you push it once and it closes, try pushing it again after that, and if you get further movement, then you know that you have to hold it to get a complete close.
On my 2003 Mini, pushing it once closes it MOST of the way but leaves the back end up a few inches for ventilation. Then I have to push it again. If I hold it down from the beginning, it will of course close all the way without stopping in the ventilation mode.
Speaking as a person who owns a 2004 Avalon that HAD a leaking sunroof, your drains are probably clogged up! The two in the rear are nearly impossible to get to but a good shop can blow them out.
Answers
On my 2003 Mini, pushing it once closes it MOST of the way but leaves the back end up a few inches for ventilation. Then I have to push it again. If I hold it down from the beginning, it will of course close all the way without stopping in the ventilation mode.