I always put the starter support bracket on, regardless of the year. It can't hurt, and it does give a lot of support to the starter. $5.00 here in USA.
Learned something today. Mine does the same fast start cold, slow crank when hot. Maybe starter is dragging. I have a good elect. motor shop close to home that rebuild my generator this summer, including new armature (wires broken all over it). I'll pull it this winter and find out.