Rear axle problem

[Fiat1980spyder]

I have a 1980 Fiat spider 2000 fuel injected turbo and was wondering what i can do about my rear axle. I've so far broke 2 of them due to the drift pin in the axle having massive up and down play. Is thier a option that i can do to this where as i can stop the pin from moving such as welding it in place? or maybe removing the the pin and installing inserts of better metal?