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No, they are competitors.
No John Deere does not 'own' On-Star.
yes
John Deere makes their own lawn tractors(mowers) in Horicon, Wisconsin, USA.
John Deere manufactures their own products
John Deere opened up his first blacksmith shop in Grand Detour, Illinois in 1837.
I own a John Deere 1458 mower and it takes an NGK plug #BPR5ES.
If you own a John Deere tractor, and need an authorized John Deere mechanic to repair it this website may help you. http://www.callbb.com/page.asp?p=What%20we%20can%20do%20for%20you!
John Deere did not create the Waterloo Boy tractor, they bought the company in 1918 after they failed to invent their own reasonably priced tractor.
John Deere's own site is probably the best place to get such parts: http://www.deere.com/en_US/parts/partscountry/index.html
John Deere 5400 is a popular tractor for farm use and has pretty food reviews. It is a small tract to use on farm so it is a good investment if you own a farm.
The specifications are far too large to list in a single post. One could look for the specifications to that particular model on the websites TractorData or on John Deere's own website.