Vintage OP purchase

[Lesnerelli23]

Hello all! I’m highly considering the purchase of a circa 50’s OP. Just wondering what kind of questions I should ask about it. I own a 2019 Sub and some other current models from various brands but I know very little when it comes to vintage.

I really love the idea of a vintage OP as my “dress watch”. I know Rolex history pretty well but I’m concerned about how well it will keep time, water pressure testing, gaskets, service history, etc. What’s the proper etiquette to find these things out? Lastly, what’s a good bartering range, like up to 20%?

Thanks!