I think on the sport models there is a collar that rides on top of that top bearing. If you have up/down play on the main shaft, loosen the set screw in the collar, and while pulling up on the head assembly and pushing the collar down to the bearing, tighten it up again. Make sure to put a dab of loctite on the set screw before doing this, so it will stay in place. It doesn't have to be pushed down with a lot of pressure, but remove the up play in the shaft and then lightly push the collar down to rest against the bearing and tighten the set screw. Should remove any play you have.
Also, in the collar has a conical side and a flat side, make sure that collar has the conical end pointing down toward the bearing.
If no collar and just a "bump" in the main shaft, there should be shims available to place between the bearing and the fat spot in the main shaft to remove play.
If you don't remove the play it won't be the end of the world, but over time you will cause some damage to the shaft bearings and possibly cause them to prematurely fail.