If that's just the electric starter drive chain you might get away with patching it up ... My brother has a knack for smashing timing cases and ignition stators on his Loncin engines ... He neatly pop rivetted a strip of alloy sealed with slicone to the flywheel cover in front of the sprocket ... but his engines weren't electric start ...
Since that engine IS an elec start ... they have a thick 18 mm spacer between the right left hand side crank case and the flywheel cover ... So you might just be able to do a Selleys liquid steel repair job ... OR a pop rivet/alloy strip repair job or a combination of BOTH if the edge of the left crank case is damaged ... LOL ...
If the oil leak is only minor which it looks like , then you might be lucky and haven't damaged the LH crank case ... IF you have ... then it's a complete engine tear down , and I mean EVERYTHING except the gear clusters ... in which case you'd better know what you're doin' ... That new engine advice is startin' to look pretty good ...
A guy brought a bike to me to check out ... it was leaking oil from a crack in front of the countershaft sprocket ... I could see instantly that it was caused by excessive chain tension pulling the sprocket shaft back wards ... You need to run a decent quality chain on these things and keep it tensioned correctly ... IF there are tight and loose spots when you rotate the rear wheel then your chain is stuffed ... it has stretched in spots from getting yanked when the swingarm passes the parallel position as a result of being too tight ... A stretched chain can't be properly tensioned and will come off regularly ... causing broken cases , stator plates and unevenly worn sprocket teeth ...