As I went through the M62 I had to ponder the purpose of this spring. All it does is puts a slight load on the bearings and being fairly high speed bearings they are not extremely tight and could use a little load. It's not a counter thrust spring as there is no thrust created. The rotor gears are spur cut which gives us that awesome whine. That bearing has the largest amount of clearance and I could see it trying to walk in the housing which that spring would aid in keeping it going the correct direction into the coupler but the front bearing has a great press fit.

If you haven't replaced these before, the coupler drive has to come off to remove the bearing.