Re Oil Stains
I think the what looks like unusually black oil stains over the wings are no more than an optical illusion, possibly related to the film used.
Below are photos of a RNZAF Bristol Freighter that I took at RAF Gan back in 1958.
The originals are in colour with the same photos saved as "greyscale" images. The greyscale black and white versions make the brown oil stains look darker than on the colour originals, particularly on the in-flight photo. The black stains appear very similar to the stains on the Lancaster in the original post.
As regards the feathering, there's an interesting thread here on PPrune:
http://www.pprune.org/aviation-histo...athered-2.html