Despite the Crimp there must be some sort of Seal under there that the Crimp squashes because Oil Pressure Sending Units from other Cars sometimes leak in the same area.

However, there is a Crush Washer between the Sending Unit and the back Plate that it screws in to.

I have also read of the Back Plate being Cracked but that usually happes at the Turbo Line Banjo Bolt area.

On a W123 if it had the same type of Sending Unit you could get at it by putting the Left Front Wheel on a Ramp or Jack Stand assuming you are not fatter than Me. I am not sure on Your Chassis.

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84 300D, 82 Volvo 244Gl Diesel