Not a dumb question - at least not to me cause I'd like to know if a CVT transmission is sealed. Can the CVT be checked, or needs to be checked, for fluid level between service intervals.
Toyota suggests you inspect it every 30,000 miles, they never suggest you replace the WS ATF. http://www.toyota.com/t3Portal/document/omms/T-MMS-12PriusC/pdf/2012_Toyota_Prius_C_WMG.pdf Owners of previous models suggest you replace it at 30,000 miles then every 60,000 miles after that. Again in previous models, there are drain and fill plugs, to inspect you open the fill plug and be sure it is full to edge of the plug. I bet the details vary on the c. http://www.greencarcongress.com/2012/02/priusc-20120208.html
Special oil due to the fact it immerses motor generators so must withstand "high" voltage. Toyota only. BTW, the same applies to the refrigerant used in the A/C system. Special oil in there too as it immerses the "high" voltage pump. The diff. is in there with everything else, and uses the same oil. There is some evidence the HSD oil is stressed and that taking care of it is a "good idea". Change it out at 30,000 mi. Cheap insurance. I was quoted $100 to change it by a dealer. The oil costs around $30. Lots of members do it themselves.
The Prius c uses the same Toyota WS transmission fluid ("WS" = world standard) as the Gen-II and Gen-III Prii. 3.5 quarts according to the Prius c manual. It's a good idea to do the first drain-and-fill at 30,000 miles to get rid of all the metal shavings that comes from the normal wearing-in process of the gears, and the dissolved metals. Hope this helps!
I don't know if this will help but take a look at it to see what it's worth. It may help and it may not. Gen1 Prius Transaxle Service I def agree w/ changing it at 30k and 60k thereafter. In my mind, its cheap insurance.
