The 518 based trans have a history of O/D issues from poor lubrication to the rear of trans, which has probably damaged the O/D planetery set, causing the whine. There is a modified intermediate shaft that is avalible that has larger lube holes to remedy this. Also, there is a spring loaded clutchpack that requires a special tool and a press to compress. I'm sure people will ring in on how they R&Red the spring, but be warned that is has between 650-800lbs of holding pressure. Other than that, the O/D units aren't that bad. I don't know of a manual, but I'm sure one of the trans rebuilders sell them.
