While investigating the toaster and emptying it's crumb tray I noticed a strange yellow-oil drip in the bottom back corner, which confused me as toast is dry so where had that come from. I think I had noticed and cleaned it before. This time I realise it also ran lightly down the back of the toaster so was not coming from the works. I looked up and notice a matching yellow-oil drip on the bottom of the extractor fan above.
Turn off power, get screwdriver and chair to stand on, take it apart, find some yellow oil and a lot of brown sticky toffee grease all over the innards. Spent the next hour removing the fan and front housing, soaking them is washing powder, cleaning the back housing with kitchen spray, scrubbing the front housing and fan (killing my spout brush in the process), rinsing it all, flushing out the front grill with IPA, more rinsing, drying and reassembly.
Looks much better, but the skin on my hands feel horrible.