Mineral , semi synthetic or fully synthetic?

[HondaCity1998]

for an almost 20yo stick with 10w40

Thanks. i'm currenly using 20w40, ayun may oil leak nanaman ako sa valve cover gasket. ung mekaniko kase nag sabi na un ang ilagay ko kaya un nilagay ko.

ano pa bang pwedeng naging sira due to wrong vescosity? thanks