OSV issue

So in my 97 740 iL, I attempted the ten minute OSV procedure in the video. I can't get the diaphragm cover to snap back on completely. Thought I had it yesterday, drove it 100 miles and it was good. Drove it this morning and it was fine until after I stopped. Refired it and the hissing was back. I have to be missing something simple, but why can't I get the diaphragm cover to snap back on to the body securely? I have big hands and can't seem to get enough force on it to snap in to place. Thanks!

OSV issue