The 371 is a clutch drive machine and as such in order to get it to turn while driving forward, you must move the steering lever on the inside of the turn, beyond the neutral position lightly into reverse to get it to turn. Sorta like having a steering brake on a old cat or crawler dozer, in this case you lightly apply reverse instead. Otherwise the tires on the inside of the turn will continue to coast along until they run into something they can't coast over and you won't turn much if at all.
Beyond this there is a forward and reverse drive clutch for each side of th machine. They are quite HD and run inside a oil bath in the center chain case. There would be a forward and reverse adjustment for each R and L side. If you pull the top off the chain case you can see the clutches and should be able to see how to adjust them. I have no idea on how much work would be involved in changing the clutches but adjusting them should be no more then a hour or two. When the steering stick is centered each clutch needs enough clearance not to creep, pushing the stick 3" forward or back should result in full engagement of the forward or reverse clutch. That is about all there is to set.
Also make sure all the bolts on the pivot points of the boom are tight and don't move when moving the boom or you will quickly wear the ears out. When the bolts are tight the force is spread over a large bushing, and when they are loose only the ear takes the abuse.
Ken