If you elect a weld repair, you'll need full penetration and a very clean surface inside and out. You'll also need to maintain roundness of the socket ID, no easy trick. I'd bet Van's gear lag sockets are reamed after welding.
Cleaning is straightforward. I'd pull the mount off the airplane and media blast. To aid penetration you might "V" the crack slightly, but a Tig usually makes penetration effortless. To end up with a smooth ID and help maintain roundness, you might try machining a solid brass plug to match the ID of the socket. The weld will not fuse with the brass. The coefficient of thermal expansion for brass is slightly higher than for steel. Insert the brass plug and torch preheat the plug and steel evenly to about 500F before welding. I'm pretty sure the brass plug will knock out after it cools, but I can't guarantee it.
Does it have a steel ring insert in the upper end of the socket, with the ID of the ring matched to the gear leg diameter? If so, does the crack extend through the ring? If the crack doesn't extend through the ring, it becomes an easy repair; just Tig the outer tube for penetration. You might still use the plug, but the weld wouldn't touch it.