I'm with Nev and Brenton.
The "oil level" screw is too high.
If you fill it this level, then it comes behind the back of the clutch as there is a nice big hole there. The chain just whips it up.
Preferably just fill to "chain just kissing the oil" level
The other method is to fill where you like (i.e. the oil level screw) and then put an oil drain container underneath the clutch area.
Start the bike and let it idle and "self level" for a while.
To check if you have enough oil, then just put your finger in and touch the (non-running) chain - if you get "oily finger" then you're good.
Or, as Nev says, take off the inspection cover when the bike is running to spot the oil spatter.
An oil tight bike is possible; I am informed.
Something that doesn't appear possible for me though .... for any length of time..
John "Josh" Nashwebmaster@arielownersmcc.co.uk
2009 royal Enfield,1978 t140 bonneville, '67 CJ750, 196-ish Ural M62 outfit, 1960 k750, ''51 kH500, ''49 soon to be Ariel bobber, 47 VH twinport, '44 Ariel WNG, '43 Ariel WNG, '41 Ariel WNG and piles of rusty scrap ....