"How are you" gets "fine". A specific question gets an answer, and an answer is somewhere to start. "Do you still have Dad's old tools?" "What was the name of that teacher who hated us both?"
A long study followed a group of Harvard men from about twenty into their fifties. The ones who had been close to their brothers and sisters when young were less likely to have had major depression by midlife. Evidence: decent
It was all men, mostly white, all from one university. And it's about the relationship you had then, not about repairing it now. Nobody has tested whether getting back in touch at forty changes anything. Evidence: worth trying
One question takes two minutes. If it goes nowhere, send another next month.
Same theme: Brothers and sisters