I can't actually see whats wrong with the stud - is it broken away from the stay?
They are quite nice frames, clean looking. Is it worth restoring? Honestly depends on how much it means to you or if you are just looking to do up and sell.
If there are no bad dents/cracks/rust, a cheap respray would make it look like new. Decals from Gil here. Could look great
Look again - you can see the post has cracked and is held on by not a lot.
Fixable by any frame builder - who will also be happy to paint it
Wether it's worth it is up to you - but those frames seem to make good money if they are in good condition - but that one looks like it's had a hard life.
Gil has the decals on file as he did some for me a while back .
you dont need a frame builder , just to fix the brake stud , just someone who knows how to weld .
afetr that a nice re spray , decals , and a full 91 XT groupset .