I'm new to the forum and am looking for some advice regarding my mother's 18K Constellation. It was purchased by my father in 1967 or 1968 in London. The watch runs, but is very slow (losing about a minute an hour) so it needs a full service. I'd like to sell it on eBay, but I'm wondering if I should send it to Omega for a full service or let the buyer handle that. I also don't know how much it's worth. I don't have the box or papers, but it certainly is authentic. Thoughts/advice appreciated.