Good news: it's not leaking washer fluid
Bad news: it's coolant
Discussions with our resident Doctor suggest it is probably the oil cooler pipe. I've not had chance to get on the ramps and have a look, so have just ordered the parts (they'll come in useful one day if not now!) and booked in with a local mechanic over the next couple of weeks, hopefully fixed and sorted in time for the annual meet.
My simple brain still cannot understand why it should start leaking being tucked up in a warm(ish) dry garage