They mark up for their labour. U see your RM20 labour sounds cheap. ahhahahaLexus Fully Syn 5W40 and Bardarhl Fully Syn 5W30 is same price at RM90. But some bought from workshop during service. Lexus Fully Syn 5W40 is around RM140-RM160. Which I find it weird as well.
Since we know workshop prices are always higher than sparepart shops.