About to purchase SS Sub Date M-Serial from a private, any tips & advise?

[Rollieboy]

Hi all,

I am about to take a leap on to the real Rollie world, after wearing a replica for a few months. For me it was always clear that I would jump into the genuine bandwagon, if the hobby took over. And it did.

I am looking into buying a new M-Serial SS Sub Date from a private collector. The seller is very reputable, and I have no reason to suspect anything. I do think of myself as somewhat knowledgeable already on telling the difference between a rep and a gen. Nonetheless, is there any specific advise you would like to offer to me on perhaps not as much as for controlling the authenticity of the watch, but rather for ensuring that the watch is in a good mechanical condition. It should be brand new, but I just want to make sure it is totally fine. Am even considering of taking it to an AD for a quick checkup. Haven't decided yet. Of course, any tips on the authenticity side (although I think I know all of the more common stuff) are welcome as well.

Many thanks from a former lurker

- Rollieboy