Weather cap issue

Never had it apart. Sometimes the part that goes into the device is a flexible “T” shape. If so, you might be able to reinsert with a pair of tweezers.

Thanks for the suggestion twolpert. The part does indeed go into a T-shaped opening but it is very tedious trying to insert it into the proper place. I'm going to try to open the plate with a tiny Phillips screwdriver and see if that works. 

Since your post is over 2 years old, this may be moot, but I've had a similar problem with the Montana 750i, twice. The second time, the cap got lost and I'm trying to get Garmin to send me a replacement

I don't know how similar the 700i and 750i are, but it appears to me that the ball that holds it in place is too small, so it pops out of its socket too easily. On the 750i, there is a plate that screws in that holds the ball in place. I had to unscrew the plate, because the ball was too large to pop back into its socket (but not too big to pop out easily). The screw is so small you need a jeweler's phillip's head screw driver to unscrew it, but it was in so tight that I had to buy a power screw driver from Amazon to get it out. If you still have the problem, see whether any of this fits your case.

As an aside, one thing I am considering is trying to make the ball a little larger using Plasti Dip, so it doesn't pop out so easily.