I don't think the market has changed that much since your first valuation. I suspect this is down to Watchfinder's desire for your piece at any one moment in time. I've also known a large variation in offer value based on who gives the offer...once having one buyer offer me about 2/3 the price of the next within a few days when I accidentally received two offers to buy. I think they work on about 35% profit and they will probably have to factor in a complete service for a vintage piece.
Have you tried other dealers like Parkers, just to get a comparison?