Calling All Tudor Experts!

[nboyer]

Hello my good people. I'm a newbie to the forum and am hoping that you experienced people can help me identify and authenticate (well, try to at least) a recent purchase. It supposedly is a Tudor Oyster Regent from the 50's. My questions are as follows:

1. The case. Does it appear to be authentic? There is no stamp between the lugs. Also, I do not notice any splines in the case tube, have no idea how the o-ring would be serviced without destroying the tube during removal.
2. The movement. No where do I see a caliber number. I cannot positively identify the movement, is it a Tudor modified or ETA?

I found this article about a 'similar looking' watch http://www.vintage-watches-collectio...omb-dial-1954/

It needs a mainspring, not sure where to begin to find one, though I do know the first step is identifying the movement! Any help greatly appreciated. Cheers! -Norm