I know you think you and your mower are unique, but Yardman's have been made for a very long time and there is more than 1 model Yardman which can be fitted with a 42" deck.
So telling us tou have a problem with your 42" yardman is about as much use as telling your lawn supplier you need something to fix your green grass.
There is also a bush on the bottom of the steering shaft that may sit above or under the gear you replaced you should have been oiling it every month which you obviously have not been doing or you would have been here several years ago enquiring about a sloppy shaft.
If it is an older model than Cars was thinking about there will be a steel bush on the fan gear pivot and yours will most likely be in 3 pieces as it is doubtful that you have ever lubricated it either and the hole will be flogged out oval requiring replacement of the fan gear, bush, and pivot bolt.
Odd that yours should get this bad strait up
Usually they will only steer left and the not right.