I've been through this many times & think it's a worthwhile exercise. I'd start by finding out the name of the daughter and her address.
I prefer to approach previous owners in writing. People generally appreciate hearing from new owners of significant cars from their past, but I think they also appreciate a little distance at first. You can imagine how bizarre it would be to abruptly hear from someone who owns a car you owned decades ago.
If possible, enclose a photo. I always include my phone number and almost always hear from them.
Make sure that you include a list of specific questions in the letter. I like to ask for things like original sales documentation, maintenance records, and some sense of its history.
I'm particularly glad I tracked down the original owner of my latest SL and heard the story of how she came to own it: In the spring of 1970, she and her husband were at a horse show not far from their home in CT. At one point, her husband asked her if something was bothering her and she said she was dissappointed that he'd forgotten her birthday that day. Of course, he apologized and they went home. They kept horses on their property, so when they got home he surprised his wife by telling her that her gift was waiting for her in the stable. She opened the doors of the stable and fully expected to see a new horse, but was greeted by an Arabian gray 280 SL. She owned her SL for the next 20 years and always affectionately called it her "gray mare."
Douglas Kim
New York, NY
280 SL #016220