Having read through other threads about battery draining I dutifully checked the boot light (nope) and then went on to the power sounder. Disassembled the wiper/scuttle to allow access and shone torch down to look for bracket nuts only to find that someone else had previously disconnected the power sounder...
That said, are there are any other common causes of battery drain or is the lead-acid lump simply cream crackered? Can't find a date code on it so can't give an accurate idea of age.
Whilst looking around engine bay generally saw some oily marks on front end of what looked like a leg of some sort. Underneath there was a hanging drip of oil on the plastic(?) tray under front of engine. Does this sound like the crank seal I've read about here... not looking forward to expense of that if it proves to be the case. Small amount on driveway - not pleasing the other half there! Once I can move the car will doubtless be cleaning that...

Oil level seems fine - but needs a change as very black - and some previous owner (perhaps the power sounder disconnector?) broke the loop off the top so had to use pliers to grip the thing! Having done that I looked for a dipstick for trans fluid - is there one?
Only other thing noticed is that the twin tail pipes are black with bits flaking off as if they've been seriously barbecued in an oil well fire. The back box itself seems reasonably sound but the tailpipes absolutely fried to a crisp pretty much.
Does this look like a back box change to lose the baked-on look?