I drive same year 2008 Myvi 1.3 Ezi. 12 years old car don't change to thin oil. Keep it at 10/30 or 10/40 semi synthetic. By this time all the gaskets and seals would have hardened. Leaks will appear.

Only last month i changed the valve cover oil seal/gasket set. Bottom has some leak that seems to come from where gearbox & engine meet. That also needs to be changed.

So if you have been using 10/30 or 10/40, just keep using that. Do remember that once you change to fully synthetic, it would clean the carbon build up at the gaskets that actually seal the leaks. And you get leaking engine oil on floor.

I kena with my old corolla and also this myvi. Was using semi syn all the while and changed to fully and oil leak. hahah.

uhh not expert but i changed my oil on my own before. try adding 100ml more and see if it increases higher than .5mm?