What oil would you use for a VW eurovan with 260K on the motor that drives 50% city 50% High way. uses about 1L of oil every 2500KM. the manual asks for 5W30 upto 25C. I was thinking of AMSOIL 5W30 but after 10K usage I have to add 4L make up oil. It gets costly. All other synthetic oils cost about the same. I was thinking of blending 5W30 GTX with AMSOIL 5W30. 4L GTX 1L AMSOIL. If you have anyother suggestions please let me know. I have access to AMSOIL, Shell, Canadian tire brand, Castrol, penzoil, Qstate, Valvoline, Mobile Trisyntec.