what do they actually do that EG Steele, a long established company, can't do by itself?
Mandy Rail are a third-party wagon maintenance company that repair wagons out "in the field" in yards, sidings, terminals.
According to their website,
E.G. Steele are now focused on the supply (and re-conditioning) of parts for wagons, so an agreement between the companies makes sense.
The E.G. Steele site at Hamilton used to be a wagon repair / workshop facility, but I don't think it's seen much use for this in recent years.
This is an interesting working from 2011, with 47739 moving former Rover KSA wagons to E.G. Steele for conversion to timber carriers:
https://www.flickr.com/photos/55624905@N07/5655522160/ (Photo: Derek O' Connor)
Cement wagons from Oxwellmains visited for pressure testing, as seen here behind 60002 in 2018:
https://www.flickr.com/photos/keithmcgovern1/25349183487/ (Photo: Keith McGovern)
E.G. Steele also had some 2-axle TTA tank wagons hired out for use as brake force on unit moves, back when deltic 55022 was in use dragging class 334 units between Yoker and Kilmarnock:
https://www.videoscene.co.uk/taking-stock
One of those TTA wagons (STL 51952) is seen on site at Hamilton in 2018:
https://www.flickr.com/photos/21513703@N06/41813977062/ (Photo: Tom Smith)
An unusual relic in the yard in 2014 was the trailer train:
https://www.flickr.com/photos/21513703@N06/11779488755/ (Photo: Tom Smith)
The topic of the "trailer train" is a rabbit hole by itself, discussed here:
https://www.railforums.co.uk/thread...-railer-wagons-discussion.278163/post-7168698
By 2019 I think the main use of the sidings was for stabling the Royal Scotsman set, as seen in this interesting view:
https://www.flickr.com/photos/scottdarg/32641666307/ (Photo: SWD Transport)
This thread on Rmweb has more info about E.G. Steele -
https://www.rmweb.co.uk/topic/142502-eg-steele-wagon-services-earnock-sidings/
The name "Mandy Rail" makes me think of Nicolas Cage and the
2018 surrealist action horror film "Mandy"