I want to fill my manual transmission with new oil soon. Vehicle is a 9000 CSE year 94, engine is B234E. I have already found out that according to DIY Manual, I should fill in mineral engine oil 10W-30 or 10W-40. Most engine oils of this viscosity class, which I found are partly synthetic. Can I also use a partly synthetic oil, or is it absolutely necessary to use a mineral oil?