On rusting cast fittings

Kayaker

Having seen some leaky joints in cast iron joinery, fortunately not mine, am compelled to ask this seemingly dumb quesiton.



Is the forebearer of a leak a rusty iron fitting and, if so, should rusting fittings be coated to prevent further rust and extend their useful life?



I'm asking because my basement from the Civil War era is full of heavily rusted (recently installed, made in China) fittings, and the pipes are rusty where the pipe wrench dug into them.