So like many others here I have developed an unhealthy interest in the Vintage Seamaster 300 w/o date. I realize I am coming very late to the game and that the purchase of said watch represents a potential minefield. I have read as much as I can in a bid to avoid the potential pitfalls however in my price range €2,500-€3,000 it really seems as if one is rolling the dice with regard to originality no matter how much they vet the potential purchases. I have seen SM300s in this price range with well developed patina but with serial numbers on the movement which are either inconsistent with the date listed by the seller for the watch or which do not match at all. More often than not the serial number is obscured by the seller. However even if it is legible absent an extract from the archives one cannot be sure if the movement is original to the watch. So my very long winded question is that supposing I am unfortunate enough to purchase a SM300 with a donor movement (ie a franken) is the watch valueless in the real world or is it liable to hold its value similar to Watch Co examples which now cost circa €3,000 on eBay?
Valueless? No but of course people are likely to pay less for a non-original piece than an original. Liable to hold value? Who knows. If you know of SM300 sales with openly stated non-original movements you can compare to sales of newly built SM300's (ref 165.0324), but it might be a difficult excersize.
I would not...not because it's franken, but because it's not what you want WIS Rule: The most expensive watch you will buy will be the watch you bought instead of the watch you wanted
I've had a few SM300's with "non matching " movements, they are not valueless just less valuable. If you're not sure when you buy it, ensure you get a good return agreement.