sealed Rotavator casing?

I have a Rotavator with Honda engine,model is pso45h,there is a problem with the dive shaft to the hoe wheels,it slips and jumps under load,the manual shows a shaft connecting the top pulley to the hoe shaft, but I can not access the casing,it is completely welded up,how do iI get into it ,do I have to cut it open and reweld it? Any advice please ,on this or where i can get a workshop manual