For some strange reason, many Rolex owners are prepared to put up with poor time-keeping. Most mechanical watches- if serviced and adjusted properly- are capable of keeping precise time.
To paraphrase an old adage: yes, you can teach an old dog new tricks and yes, an old beaten up Omega from 1962 can perform better than COSC, -4 to +6 seconds per day. (COSC stands for "Contrôle Officiel Suisse des Chronomètres", the Official Swiss Chronometer Testing Institute).
Let's say, your new BMW 318 fuel consumption is 30L per 100km driven @ 80Km/hour. Would you put up with such a poor performance or would you take it back for further tune-up?
If your NEW Rolex is + 5 or +10 sec a day, take it back to Rolex and demand for better performance.