Re: oil injection removal '85 merc 150
You need part number 43453 if it is available. That retains the pump driveshaft bushing and plugs the hole where the pump mounts. Then remove the oil components and the warning module. You'll also need to remove the fitting that the oil tank pressure hose attaches to and plug the hole in the block.
Order three stickers (37-818029 1), one to mount near the fuel fitting on the motor, one for the dash, and one near the fuel fill fitting on the boat. They'll alert the operator that the gas needs to have oil added. One frequent problem we see here regards the infamous "brother-in-law" that forgets to add oil to the gas and roaches the motor.
You should probably replace the fuel lines where the fitting for the oil T's into the fuel line with a single piece of fuel line.
I don't typically advise removing it, but I understand your concern considering the plastic drive gear in a 20+ yr old motor. As they begin to fail from wear, they still turn, but skip a tooth on occasion. The rotation is adequate to satisfy the motion sensor for the warning system. But it gets worse and pumps inadequate oil eventually and the motor fails. They're really quite resiliant if the motor doesn't overheat and if they get plenty of lubrication. But somewhere in 20+ years, you almost have to have had at least one overheat.
