I would contact the manufacture and ask them for help.
It depends on which gun. Different guns assemble in different ways.
The SIG Sauer P226 has been modified for suppessor installation.
Gun shop or gunsmith
Best left to a professional.
see the link below
it depends on the model.
Look up on the Web under "Air Gun Repair" and find a shop closest to you.
"The proper way to clean a gun is to make sure it is not loaded, spray it with cleaning supplies to get all the gun powder out and then put it back together."
What an answerable question. You have provided oodles of information
Generally no, but it is important for proper maintenance that the gun be dismantled, cleaned, and lubricated after every use in order to get the most of out it.
If following the instructions in the owner's manual doesn't assist you, I suggest you take it to a gun smith/gun shop.
See the link below for the drawing.