Help! What's the white glue coming from Celestion SL600SI

Any misstep could easily ruin the speaker, I would think.

So long as your not a klutz, it will be fine, and you can reseal with more white silicon if needed.
And it’s only the sealing compound, not any capacitor electrolyte. The white stuff in the video shadorne posted is just white silicon fixing compound to stop things rattling around, and nothing to do with capacitor electrolyte leakage.

Cheers George

@shoubang   

+1 What George said.

I've owned 4 iterations of Celestion SL speakers, and it is easy to remove those 2 front plates with an allen wrench. I have done so many times for different reasons, and I've never seen anything like that. I doubt that it's the crossover. The crossover in these speakers is at the bottom of the box, and it's shielded by thick foam. It might be something that the previous owner put behind the plate for some reason. Screw it off and investigate.  

@shoubang  

Hint   @shoubang , it's only the 4 bigger screws not the 3 smaller inner screw that need to be removed. 
And when you screw them back, just a little nip tight or you'll crack the plastic mounting plate if your a gorilla and crank them down.

Cheers George     

georgehifi,
If you're talking about the ribbed plates on the front baffle, they aren't plastic, they're cast aluminum.