It is definitely recommended to check the oil level when doing an oil change. Here is a link to the owners manual for the 2023 GasGas EC 250 if you want to check that out and see the service schedule and maintenance procedures. azwecdnepstoragewebsiteuploads.azureedge.net/23_3215102_en_OM.pdf
Also when you drain the oil you never get 100% of it so the amount you need to add will vary slightly. It's best to remove the oil cap when you drain the old oil and remove the check bolt when adding new oil. Once oil starts coming out the checkpoint you know you have added enough.
Sorry I'm new to this. I'm so confused. So why are you checking gear oil when this video is about transmission oil change. But then filling it in the engine oil whole? Is engine oil the same as transmission oil and gear oil?
On a 2 stroke like this, the engine gets lubricated by mixing the gas with oil. But the transmission and clutch use the same gear oil like shown in this video. Hope that clears it up a bit!
Probably not very much depending on the bike you may notice it shifting a bit differently at first. But most bikes will have a vent that excess oil can drain from if filled too much. As long as you have enough oil to come out of the oil level check bolt, you will be fine. Hope that helps!
