Uneven wear on rear disc brake pads

[Raggety]

Hi all.
Please help.
My Capo 1000 ( 2004) rear break caliper started leaking. Thought it was because using brake fluid that was opened about a year ago , when I replaced the rear brake pads.

On losing the rear caliper, i noticed the inner pad was about totally used(very thin part left over) while the outer pad was minimal used.
Do you think it is a sticking caliper piston , and what would cause it?

 

[Bill the Bong]

 

[Raggety]

 

[Welsh]

 

[Raggety]

 

[Jughead]

 

[Raggety]

 

[Raggety]

 

[Raggety]

 

[Stevie]

 

[Jughead]