Make sure to get it serviced by a good professional watchmaker. And most of all, make sure they do NOTHING to the case or the dial. No renovation, no improvement, no machine polish, make sure they do not touch the outside.
Only service the movement, which means take the movement apart, clean it, put it back together and regulate.
The beauty of the watch is that it is very much like when it lwft the factory. When people use polishing machines on a watch, it causes damage because it removes all of the fine detaols and the angles. Your father in law’s watch is in very good condition and needs nothing but a movement service.