welcome to the site
I am guessing this is a solid read axle, and NOT a IRS model,
if so, then odds are the rear axle splines are stripped, what happens is the left side wheel bearing seals fail, water gets into things, rusts splines on axle, and then get soft and strip very easy, this is a known weak link on all honda solid rear axle 4x4 atv's
the left side only has one bearing seal, right side has two, thus the weak link is the left side.
Good news is, its not that hard to fix, but not that cheap as a new axle is about 200 bucks, but once done its good for a while, if you keep an eye on wheel bearings in the future and replace before they are bad for long!
as for where to get a service manual, I like REAL hard copies, I BUY mine from Honda, but used one's can be found in places like Ebay, and I gather (facebook(I don;t do face book, but hear they sell all sorts of things there)
I am sure others here can chime in on where to download one for free too if you like that way!