i have a mercury 50 hp 4 cly. ser. no. 7031920. im not sure of the year, mid 70's i think. the shift shaft broke off at the water line because it rusted through, i have the motor torn apart, and right under the carbs where the shaft comes out from the lower end there is a bracket , what is holding that shaft in, i need to take it out and replace the whole shaft. is there a pin, or an hex screw?