Mike, have you tried carefull muscle training? Or is it advised not to use it?
Not using something úsually makes things worse over time; stiffness, reduced muscles and reduced flexibility, etc. The guy at our gunclub damaged his shoulder with several car accidents. He's training twice a week now, and it helps he says. He's still shooting with it. He's about 50yrs old.
What does a Gamo Compact weigh? Maybe try with lighter pistol?
Just thinking outloud here..