Daewoo Lanos (98) 1.4 i - rusty sills - zookeeper

hi room, was doing the pre MOT check over, apart from the split in the back box i noticed the sill rear of driver door very bad, its the car outer skin that wraps under the sill thats gone

but its solid underneath that, so is it cosmetic or a fail?

the chassis rails are solid and the seat belt anchor points are more than 30 cm away from the corrosion, can i get it filled with p38 and rub it down and a quick blow over with some paint? thanks in advance zoo

 

Value my car