Hi.!after oil change to 5w30 from 5w40 I see leaks around the engine..not something terrible but before it didn't have such a tpt with the 5w40..to turn it to 5w40 or 10w40 and for less noise from the motor
The change in oil weight would not cause an oil leak. Are you sure whoever did the work tightened the oil filler cap, inserted the dip stick in all the way, did not under or over tighten the oil filter, and tightened the oil drain plug to the correct torque?
I use since years Mobil1 5w40 turbo diesel oil - it has the same additives as the high mileage Mobil1 oil and I drive in the same temp range like you...
This year I will fix my oil leak - 1 tiny drop daily from the valve cover gasket! Sure from there the drop goes down the engine or when I drive it drops on the cat or exhaust.
No fun to change the valve cover gasket thought. If you have to change your valve cover gasket you should change the spark plug tube seals as well.