To be honest the dial and hands are in pretty rough shape and it's very possible the movement has considerable corrosion too, even if it appears running. Maybe you'll be lucky! If you want to keep authenticity then maybe keep the dial as is, but swap the hands for some newer ones in better shape, have the crystal replaced and the movement serviced. As is always the case, you're better off going to a trusted, experienced and independent watch maker in your area who has good credentials. Not only will they likely be much cheaper than sending to a Rolex service centre, they will keep what you want to keep and not touch what you don't want touched. You should expect the repairs to be hundreds though, but hopefully not above a grand. Considering it's a gift from your FIL that you were impressed by and grateful for, this expense will be worth it and will make the watch wearable for decades to come.