E-Z Wiring #20 Fuse Box Issue

[SRA1]

I lost my gauges last week and had to dive into the electrical system for the first time. It has a 20 circuit E-Z wiring fuse block. When I removed the cover, the mini-fuse for the gauges was missing. Turns out it was stuck in the top of the cover, in some rubbery sponge. The sponge was apparently holding the fuse in the slot. When I tried to re-insert the fuse after checking it was good, it wabbles back and forth and falls out when I move the box back into the mounting position. I don't see any breakdown, diagrams or pictures on opening the fuse panel itself in the installation manual. It appears that the tabs\connection repair would have to be fixed from the bottom of the panel. Any guidance on how to open the fuse box or repair the individual fuse holders would be greatly appreciated. The box is pretty tight against the firewall, with wire bundles going in all directions, so I don't have any slack and there is no room to work. I can't figure out what holds it together, or, more importantly, how to open it. Thanks.