[pkulak]

The modern movements are a lot more robust. It wouldn't surprise me if a 50-year old watch had 1 year as the recommended service interval.

[Domenic_S]

I can't find the original source but Scott @ TRF says the calibers in 50 year old rolexes have a 5-year service interval: https://www.rolexforums.com/showthread.php?t=679777