Repairing my MYOG wind shirt

Unstitch the sleeve at the arm-pit and make a new sleeve.
Then sew the new sleeve back on.

sew the seam back just to close the hole

then sew a strip on the inside for strength

or iron on tape from fabric store

or use McNett seam grip to strengthen it

when you sew a french seam, sew an extra row of stitches on the inside for back up. That may prevent the row of stitches from ripping out, or if it does, that extra row will take up the slack.

I usually sew an extra extra row too. If you were doing this commercially, it wouldn't make sense because it would take too long. It takes a tiny amount of time compared to fixing a hole later.

Thanks for the answers. I'm gonna try Jerry's idea, and if that doesn't work, I'll remake the sleeves. That's an interesting idea adding an extra row of stitches to the french seam. I have used diygearsupply's French/ flat felled hybrid . Would there be any difference in using that versus two rows in a French seam?

did you do a flat felled french seam?

that would be better, because you have two rows of stitches equally sharing the load

if you do an extra row on a french seam, it will take no load until the first row starts to give

with a flat felled seam I also often do another row of stitches

is your fabric very loose and susceptible to fraying? That would make it more difficult to get a strong seam

with a regular flat felled seam (sometimes called a faux flat felled seam) you sew the two pieces together, then fold over the raw edges twice and sew them, hiding the raw edges. You can cut a strip off one of the pieces of fabric so you only have to sew through 4 layers rather than 5. That's what I do for seams that require strength, like a tent. I don't see an advantage to doing a flat felled french seam.

with a french seam, the row(s) of stitches are hidden. You see nothing on the outside. You're putting fashion over strength. That's what I do for clothes, just because that's what I've done before if for no other reason. Strength isn't an issue. Having the row of stitches hidden is good for waterproofness.