Dont know why they perform so poor its surprising what you tell about shell one's as well. I thought it was only Zic M7 10w40 so pathetic.
I have not tried imported 10w40 engine oils but they must be good as you are saying bro and Suzuki may give it try in future. Actually i believe 10w40 would be good specially in winters or even in summer but in Zic case has proved worst. Zic m5 20w40 is very good engine oil and grade 20w40 is good all rounder to Pakistani conditions.
I nearly damaged the chinese 70cc engine seals there were coming oil seepage stains from head cylinder seal. Which have stopped now now after switching to Zic m5 20w40. Zic m7 synthetic oil either it is lower quality of seals or one year old engine is too older for synthetic oil. But i think seals quality better be blame synthetic oils are widely being used there is this complain with synthetic oil leaking seals but with older engines in cars. May be one year old chinese 70cc engine proved too old for m7 but this oil does not like pridor & gs as well
I have apologized to poor chinese engine for cruel m7 10w40. She is loving m5 20w40 no doubt very good engine oil my favorite.