shouldn't need a new rebuilt with 1300 miles on it,as said above,it depend what ratio those miles was put through,
normally i'll run the first 200 miles at 32:1 or 40:1 oil ratio,then check spark plug reading,,those engine run best around 42:1 tough...

 

The 400 motor does have an oil bathed counterbalancer, honestly its good he maintained this as they are not a cheap item to replace. given the age its time to do a top end job, the factory pistons tend to crack up easy and get in the crank case. do it now and you may not have to do a bottom end for a while. if it cracks it will grind up in the crank case and cost twice as much to fix or more.

clean the carb and it most likely needs new clutch buttons drive and driven and a belt change.

 

Ok so now where is a good place to find a cheap tech manual for this thing?

 

no cheap place I know of, but the polaris shop manual is way above the haynes one, its very detailed and has saved my rear a couple times.

 

The Polaris atv 1985-1995 from CLYMER is very detailed and easy to read. It costs $20-$35 but is worth evey pennie. It is what i am currently using to rebuild my 1986 Polaris trailboss 250 4x4.

 

A filter cleaning, new plug and viola it runs good again.