Those cowlings alone are " hefty " in my opinion.------Got one of those for free last fall at a dealer.-----Only thing to do on those is a complete teardown !
???----The plastic drive keys / bits last for 20 years or more.----Your motor is " special " I guess.----And perhaps your motor does not have a 1982 lower unit.----And there may have been 2 different plastic keys.----Some " club fisted " person installed the wrong one ?
Many years ago I worked in a tire factory ( quality control ) ---Today I tell folks that ----" they are all black , but they are not all the same "------Today I say the same thing about impellers.------Put a new one in at least every 5 years.