The attachment point that goes into the dovetail cut on the bottom of the barrel had most likely bent. My '76 1894 44 mag is this way, it's a stamped steel part and recoil had bent it, I cold bent it back, but after a dozen or less hot rods it bends again, and loosens up. I'm eventually going to replace it with a newer version that is machined out of a solid chunk of steel, but I'm affraid it may start shearing screws off.
Get the screws in straight and snug and you’ll have no need to worry about shearing them. I’ve built north of 100 Marlins in 50AK and never had one shear a screw from recoil. Good idea replacing the tenon though, the sheet metal ones were a joke.
