I have always used 5-30w in my 1999 Nissan Quest. I cannot see oil leaks caused by change of oil. Leaks in general are caused by seals/gaskets damaged by continuous cold/heat cycles. Rubber looses elasticity, shrinks, becomes brittle and cracks. With 102K, I would expect leaks at valve cover gaskets and oil pan. Remember, if oil is too heavy, it will not provide good lubrication in tight tolerance contact points and wear will accelerate at those points.
My van is 192K miles now. Points of leaks that I have repaired so far, valve cover gaskets (around 120K), oil pan (around 140K), transmission oil pan (preventive replacement), distributor mounting O-ring (around 180K). Other gaskets: intake manifold (around 85K-coolant leak), air-intake collector, throttle body, and EGR-Valve. I have not replaced any engine oil-seals so far and have NO leaks at this time either.
I have been using full synthetic AMSOIL that I replace every 15K miles or one-year, whichever comes first.