I still disagree but I'll post that at the end so as not to confuse...
There is an article here that looks like a good solution if you don't want to remove upholstery:
http://www.accuratebuilding.com/publications/recipes/carpentry/broken_furniture_leg15.pdfIn a nutshell, you tape the leg together, drill a few small holes holes with a nail until it protrudes out each end of the crack - then glue (altho personally, I might glue first in this case). Once dry, you clip the protruding nails. This would be good in this situation since the majority of the break is at the top and you can embed the nail into the side of the chair, clip the nail from the front, countersink and cover with matching filler...
My main issue with only using glue is that I wouldn't trust it for safety since it is on a load bearing part of the chair. Maybe liquid nails but I would still want reinforcement -
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The reason I think the joint needs to be checked (sans it's upholstery and inner hardware) goes to the cause of the crack in the first place. There is a good chance it is loose- it's an old chair. If it has a little wiggle, the force (of sitting in the chair) is going to be spread sideways or backwards (as in this case) vrs straight down. Webbing used internally does wonders for hiding how loose a chair really is and just a little wiggle would redistribute the load.
To clarify, I'm not saying take a hammer and chisel to the thing, I'm saying remove the upholstery, springs, etc grab it on both sides with one hand and give it a good shake. If you can loosen the joint in that manner, it needs to be repaired - and again, was probably the cause of the original crack... Think about how you get up from a chair. You exert pressure on the front legs.
If the joint is tight, AWESOME!! At least you don't have to worry about it re-cracking. In addition, removing the upholstery will give you a better surface to clamp (unless you have bar clamps which many people don't). Cost of upholstery will be somewhere in the neighborhood of $10-$15. For me - it would mean peace of mind and I could chalk up the original crack to prior trauma.
That said, we may just have to agree to disagree