That's a great cast iron pump...easily rebuildable and will last another lifetime.
Check the tank...have local jurisdictional boiler inspector do an ultra sonic test on it...you might have to tote it to him for a free courtesy test.....sound lowest part or tank for remaining thickness and compare it to top of tank.
They rust from inside out-oil or no oil-they rust and thin...then they rupture and go straight up thru the roof..yup, they do and as a Boiler Inspector I've investigated many that have.
As a guide, my current employer, the feds, smartly give air compressor tanks a 30 year life where they then demand we replace them...their instruction is inked in Human blood and machinery downtime.