This is the yellow parcel van from 7735 converted to a track cleaning utility van.
The local train modelling shop gave me a block of gritty but malleable and soft stuff for cleaning track. At first I used it manually to polish the top surface of the track and was surprised to find how black it got - you can see it on the edge of the block in the photographs.
It did make a difference to the running of the trains though I've since heard that the power pick-up is from the edge of the rail and not the top surface!
Eventually I got tired of doing this manually and decided to modify one of the parcel vans. Yellow is traditional for track repair vehicles - so yellow it was.
Every now and then I run this van behind a switch engine for a couple of hours on each main loop. I press the pad manually onto the track to start with, and have used the track weight bricks for added friction. I run it as slow as possible - for an hour or so in both directions. I still do the sidings and branches manually.
However I do think its effective ... and quite cheap too!