Hello guys,
So it's been a while now since my last update on this post.
The repair guy was supposed to come at my place (and then we would have had a beer!

but he came... I tried to call him few times and nothing. So I just gave up on him and decided to get the sub repaired either by myself either through an "official" repair store.
So tonight I opened the plate and I figured out there used to be a cover but it is not here anymore! (there marks of glue forming a square around the electronics and 4 unused screws positioned at the 4 corners around the electronics.
So now I am thinking of finding a way to seal the box. Should I find a proper cover that will fit the plate or can I manually fill in all the screw holes, connectors and switches? Are there any risks doing this?
I am thinking of the speaker plugs : if I fill them with silicone would not they be unusable ? (right now, I don't care because I am using a RCA cable in the line in plug, but if I decide to sell it later...)
Finally, what sealing/grease product should i use when remounting the plate (for the last screws)?
Again, thank you very much for all your advices and opinions.
Olivier