Final drive oil leak

[Yoni159]

https://ibb.co/Z6hSSM2t
I saw it i have leak on my rear wheel do i need change the oil seal inside or i need to open the gear case?
And i drained the oil and it was 100ml.. for kymco downtown 350 ita recurring 210ml so i drave with half of the amount but only for 10km... This is could ruin my gears? Because changing gears its expensive

[Ruffus]

Perspektive looks like you just change/ install this alu/copper washer.
Start with refilling 160 ml,
ride,
then 180 ml,
ride,
not more than 200ml at all, otherwise it might exhale into your airfilter, render it clogged.

As said, check the breather tube from gear to airfilter whether full of oil or not.
If there were really 100ml in it,  plus leftover, I don't think any demage were done, if there wasn't any before.