An Agar from Argentina, now living in Chile. Have a limited family tree that includes most of the people you mention, including the Fergusons. Can send you a gedcom file if you would like. My e-mail is firstname.lastname@example.org Would also like to contact William Ferguson, who you have been in contact with, re: Second Lietenant Agar.
I am mortified that you describe Agar Cross & Co. Ltd. as a 'windmill manufacturing and spareparts business', it was one "hell" of a big importing company in it's heyday.
My grandfather was William Annesley Agar, brother of Thomas Forrester Agar, both founders of Agar Cross & Co. Ltd.
Please keep in touch, as would like to fill in large gaps in my family tree.