Here is a Webley Senior.
A lovely air pistol; heavy, well made with a nice blued finish.
Please see the parts diagram provided.
( This is from a company that supplies vintage airgun parts; https://www.gunspares.co.uk/products/24544/Senior-Pistol-1935-64/ )
Links to information about these guns.
Step 1: Do Not Remove.
Step 2: Remove Barrel Joint Screws.
Firstly, check that the pistol is uncocked.
Remove the barrel joint stop screw. ( this is missing on mine, but that is ok if you regularly check that your barrel joint screw is tight).
Remove the barrel joint screw.
Step 3: Remove the Barrel.
Remove the front end of the barrel.
Remove the back end of the barrel.
Step 4: Remove the Spring and Mainspring Guide.
Undo the mainspring guide with a soft tool ( I use my wooden spatula).
Brace yourself on the last few turns, as the spring is under tension; not much though.
Step 5: Remove the Piston.
The piston can be seen through the slot in top of the gun.
Push this out with something like a screwdriver; the trigger has to be pulled to allow the piston to slide out.
Step 6: Put It All Back Together.
Grease the piston.
Put the piston and spring back in; remember to pull the trigger to allow the piston back in.
Screw the mainspring guide back in; one way to do this is to put a cloth in the palm of your hand, put the mainspring guide on this and then screw the pistol onto the guide, making sure not to cross thread it.
Step 7: An Extra Bit.
this is only to be expected with an old gun but I did read that the Little Link can be reversed to overcome this.
I knocked out the link pin, starting with a punch and then I used a cut down bicycle spoke.
This worked for a few shots but then did not seem to do anything so I returned it to its original position.