http://i.imgur.com/wHT11xG.jpg
I have several joints in my Glass Blocks in my shower that have deteriorated. Most of the window is alright but there are several places where the grout has cracked or broken off like the right side of the picture. There are a couple place where the entire joint has broken off and dropped into gap in the middle of the blocks. One joint in particular, shown on the left, has broken into pieces. Even the plastic spacer has broken. In that particular one it is apparently broken on the outside as well and wasps are coming in with some dead inside the crack.

I am confused about a few things:

Should this grout be replaced with Silicone, a Glass Block Grout, or something else? If grout, would I need to remove all of the grout and re-do the entire things?

Do I need to try to remove the pieces that have pushed into the gap (Not sure if they will fit trying to pull them out?

Do I need to insert a new Spacer or just fill the space (seems like it would be difficult to get them in there)?

 

Picture is not clear, if it;s mortar just scrape out the loose material mix up a small batch of wet mortar and squish it in the joints.