Grease and/or oil the linkages and other controls. Make some adjustments to maybe the brake and clutch controls and see if that helps. It's been a while and I do not remember the name of a powder (quicklime?) that you can dust onto the brakes to help clean rust and oil or grease off them. Some others here can probably help with that. If the crane has been sitting and not used for a while, you may have to remove and clean out some bearings and bushings that have accumulated a buildup of dried out grease and dirt. Likewise, if the swing gears have been lubricated with Crater Compound, they will likely need to be scraped or steamed and new compound applied.
Otherwise, most of the older cranes can have worn out or damaged friction bands relined by custom brake reline shops or crane dealers. Usually that is all that is needed as the drums rarely become damaged to the extent they need to be replaced. To make up for loss of drum dimension, the frictions can be installed oversized.
The dog clutches for steering may also be clogged or stuck with old grease and dirt. They may need cleaning and relubrication. These old cranes were built with a lot of toughness and simplicity. If the engine and various gearboxes are ok, you should be able to bring the old gal back to life.
The more the crane is worked, the better it will run. Good Luck!