Depends upon where it is leaking from
If it is leaking from cracked side walls then it is fit a tube time
If it is leaking from a hole in the tread then it is put a plug in there time
If it is leaking around the valve it is 50:50 and depends why
Usually it will be because rust is preventing the valve making a good seal
In that case you either have to remove the tyre clean the wheel & repaint it or fit a tube.