Need Help! Spacebar issue with Underwood Golden Touch

Dear Fellow Typospherians, I need some help. 

Recently I bought this a great great Golden Touch--well-engineered, snappy and in rare turquoise. Another good reason to be a fan of American typewirter. My favorite typer now! Look how it nicely fit into my humble adobe. 

However, this great typer needs a bit TLC. To be more preice, the spacebar of this machine is not very responsive. When I hit it, I have to hit it very hard and even so, sometimes it doesn't work. 

I took off the back-side wall to check the escapement/carriage advancement mechanism, but seems everything is just fine. Nothing on the surface is broken or missing. I guess maybe some spring is missing because when I poke the escapement piece, it moves perfectly well. Or maybe the level beneath cannot hit hard/high enough to hit the advancement piece? I don't know. 

I need some help. I can't put up with something that is not perfect. Please help me preserving this great great American typer! 

Some more pic for your appreciation: