Positioning Arm Attachments

Question: are the left and right arms of an avatar different sizes?

I have made a prim replacement for an arm, and when worn on the right upper/lower arm it looks fine. The problem arises when I try to mirror it on the left side. No matter what I do, or how much I tweak the attachment's position/rotation, it always seems to drift away from the shoulder when the avatar stands. If I do manage to fix the shoulder alignment, the elbow joint then suffers - which puts me back at my starting problem.

Has anyone else experienced this?

I dont know iuf you have tried this, but split that arm into two or three sections and wear them separately!
Shoulder/upper arm/forearm....leaving hand for weapon/item use!

If u already tried thi, then im soprry for stating the obvious
good luck

Yeah, I know the arm is three parts. My post was mostly dealing with the upper arm segment. I've since come to a compromise with it so it doesn't look outright terrible, but still misaligns during parts of animations.

Thanks anyway.

If you aren't already, use the "attachment" alignment grid - it makes things a lot simpler.

Edit window, "Use Grid" on the top right, then go to "Ruler Mode" a little lower, pick the "attachment" option in the drop down box.