Stop fannying around and take the box off, the cable is easily taken off, even without disconnecting it from pedal first, just pull on arm, whilst pulling cable thicker part through the hole till it exposes the thinner part of the end nipple so it can be slotted into the larger hole to come out.
Measure around the prop so you know the size of the inside of the seal, get a cap from a tin of some sort, and use that to cap the end, build up with tape if too small, won't lose a drop that way.
tabetha