The Tudor line prior to around 1990 was all Rolex except for movement,Tudor watches are made by Rolex. The major difference between a Tudor and a Rolex is that Rolex contracted the manufacturing of the movement out to a 3rd party manufacturer (ETA in 95% of them) much like Rolex did with there chrongraphs before 2000 they used ETA Valoux and Zenith movements. The ETA ebauche movements were made to Rolex's specifications and signed Tudor. This movement was then sent to Rolex where it was assembled into a watch with all Rolex remaining parts (Rolex case, bezel, strap or bracelet,dial, crystal and crown, seals, etc.). These parts were the same parts used in the Rolex line of watches. The Tudor movements are high grade 17, 21, 25, or 26 jewel Automatic or Manual movements which when correctly cleaned, timed, and oiled, will keep time almost as well as any normal Rolex would but might need more regulation over the years.
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And today the only step down in quality with Tudor watches in general is the price.The the main difference between a Rolex Sub and say a Tudor Sub is they used a top range Chronometer grade ETA a first class all in-house built movement but not Rolex made,and in watches like the Tudor Prince they used a light Oyster bracelet, on Subs they used the heavy Oyster bracelet.
The Tudor line are still made in the same now highly automated factory as Rolex.
