Hi nelbur, thanks. I did think of getting a very small neodymium magnet on the end of a piece of bendy wire to try and fish for it but the narrow aperture/slot is directly half an inch below a camshaft pedestal so a regular magnet on a telescoping rod wouldn't be able to fit in the slot so as to be able to plumb the depth. Looks like I'll be dropping the sump when the rain stops.