Can we be sure this is O. leptoplasta? The specimen seems to lack many of the forewing markings which seem characteristic of this species in named examples of this species I see online.
Whoa there. Who said any ID from a photo showing only forewings is certain? O. leptoplasta is variable, and is basically brown and rounded, and is one of the few Acontiinae occurring around the ACT area. But 'no', Actually: I think I see upturned labial palps, and maybe we should look in Gelechioidea. Maybe Tortricopsis semijunctella
I think your suggestion of semijunctella is correct - the faint two diagonal markings on the forewing match that species as does the palpi shape and size. and the shape of the outer edges of the forewing.