Dutch, did yours have curved face wheels to begin with? Sorry that I didn't have a "before" and "after" picture for you.
Perhaps mine was an oddity, but the face of the original caster wheels (the surface in contact with the ground) was flat, not curved. That meant if the wheel was turned at all from the direction the mower was traveling and the wheel made contact with the ground, the egde of the wheel would occasionally cut a nice furrow in the ground rather that castering to be in line with direction of travel. Now with the curved faced wheels, if that same situation occurs, the wheel should more gracefully skid over the ground with out damage.
I'm stretching my memory without having the mower nearby, but I think originally it had the same wheels on the back and the front.
Finally, the addition of the grease fitting should allow the caster to operate more freely.
Hope that helps.
fud