I didn't see a thread for the tunnel cleaning train do apologise if this has already been answered. But when did the unit stop running? I came across this video on YouTube of it in operating in the Inner rail.
"The train was successful at cleaning tunnels but went out of operation due to unreliability and high maintenance and operating costs"
"Removed up to 1,000kg of waste per kilometre in heavily contaminated areas, but typically averaged 600kg/km across the network"
1938 tube stock ... heavily modified! I recall seeing it at an Action Depot Open Day (April 1983, I think) and somewhere have photos which have not yet been scanned, so therefore are also not online / I cannot share them here.