nothing lasts forever, this includes shift and throttle cables. if cables are same vintage as boat, its time to replace with some new ones. disconnect, measure and replace with same size--buy quality cable!
steering: mechanical/cable or hydraulic? if mechanical, have a close inspection and see if system is worn out or just needs some TLC and lube. if hydraulic, i'd start with seeing if it there is air in the system (usually you get a "staccato" like feel when turning helm), check helm resevoir and add oil as needed and bleed system (use a clear hose off the nipples into a clear clean bottle; buy the kit for the oil bottle {short hose with fitting from oil bottle to screw fitting of helm resevoir}). if you have to add significant amount of oil, check for leaks at every fitting and at the helm. inspect the hydraulic ram mounted on the front of the motor, these are very durable but again, nothing lasts forever.