The 80 micron is the gold plating depth, this is actually quite thick for plate but obviously not as desirable as solid gold. A 12.3m serial model would be from circa 1951 as you suggest. If you search on the model number 2497 you may find further info (you can skip the iteration -8 which isnt important).
As for price, maybe think low hundreds of USD, Euros or GBP. It is a classic design but the plated case will hold the value back a little. Personally I wouldn't worry about the crown, sourcing and fitting the correct one wont add the value it will cost. Just get it serviced and wear it. Be aware though that it may cost nearly as much to service as it is worth so it will be a labour of love.
It sounds like you are winding it correctly but if it needs a service (and it probably does looking at it) then I would leave it well alone until that has been done.
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