I'll echo other comments here that mention age contributing to RC problems. I strained my RC and the ortho attributed it to a bone spur which, he said, comes with age

With rest and rehab you can get back to 100%. The biggest problem is going to be sufficiently resting it so you don't re-injure it and go back to square 1, or worse. In my case, it took about an entire year to get back to 100%.

Since then I've had to modify my training. Things I could do at a younger age, like flys and bench press, now cause discomfort. Now I train around it and do overheard presses which seem to help keep the shoulder joints strong, too.

If you're interested in a good read on the challenges of staying strong while getting older, check out "Strong Enough?" by Mark Rippetoe.