85 delta Info

Hey, New the forum, I have just bough a 1985, 4 door oldsmobile delta 88. I have owned a 4 door 81 Pontiac Parisianne before, same little quirks that happend with the pontiac I am finding out are commin with the delta ie window motor. There are some rust issues, on bottoms of all four doors it is heavily rusted on the inside layer of the door, the out side of the car is in very good shape, inside trunk down along the rear quarters no rust at all. some people say I should just rust mort it, and I have never eve heard of the product, just wonder if any one has ever used it before, or have any other random information on the car. Thanks again