The radio that is for a 1953 GMC or Chevrolet truck is quite distinctive. There are two models that look similar that will fit the truck. Can you post a photo or the model number?
Generally speaking the paper or wax covered and the electrolytics ones which are in a can, need to be replaced. The vibrator should be replaced also along with the associated capacitor. There is no string in that radio for the tuning mechanism. What you are describing is likely slippage in the clutch that is used in the rotary control. When you push on a button, a clutch is disengaged so that the button can move the tuner. After the button is released, the is engaged again for rotary control. The rubber inside the clutch goes hard and fails to provide proper friction. I replace the clutch disc with one made from yellow rubber kitchen gloves.
I have helped some members rebuild their radios using Emil and private messages and I would be happy to help you too if you desire to do that. They are a nice performing radio when they are restored.
I have had digital AM available in both my present modern car and the one before it. So far there is no content to tune into. I personally think that it will be a long time before analog AM goes away. When I tune into the AM band late at night, there are so many stations available that some seem to be overlapping.
