Photos and machine might be helpful?

 

Model number is in the title.
I'm having problems getting the picture from my phone.

 

Model number is in the title.

But not the make... Ariens 921047, I presume.

 

Sorry...For some reason I was thinking this was an Ariens Forum. My apologies for the seniors moment.

It is a Ariens Deluxe 30
Model 921047

 

Just weld it up and grind it down, unless of course you have a lathe setup available. Sometimes you can get a local trade school to do it.

 

Thanks for the reply.
The picture shown is after 3 winters.
The replacement shaft that has seen one storm is already showing signs.
I'm really looking to address the problem so I don't have to fix or replace the end result.

 

Same issue with my 2022 Pro RapidTrak idler shaft (Pinion shaft). Grease was getting into the shaft but mainly exiting at the chassis and not the end of the gear. The gear assembly should slide sideways on the shaft but was stuck in one place. Took the shaft out and there was old looking grease but the grease hole in the shaft was not flowing the new grease. Cleaned up the shaft and inside of gear and removed bushings. The wear on the shaft was not nearly as bad as the OP's shaft. Bushings were like new but I replaced them anyway. The shaft seemed to be worn on the underside (closer to drive axle) so turned it 180 degrees and re-installed. The gear and chainring assembly can now slide sideways on the shaft as expected. Ordered a new shaft and more bushings.

Checked the drive axle and the short axle would not easily pull out from the long axle, and was not fully seated. The long axle was quite corroded where the short axle fits. Cleaned both axles and greased them. Lubricated the chains and gears. Axle and track subframe bearings were good. Reassembled the axles and greased hubs, and the axle can now move sideways for proper alignment. Reassembled the Tracks and all seems well, quieter AutoTurn.

Bought a new idler shaft and bushings for replacement next spring. Quite surprising for a 2 year old machine with only 126 hours on it.

 

Same issue with my 2022 Pro RapidTrak idler shaft (Pinion shaft). Grease was getting into the shaft but mainly exiting at the chassis and not the end of the gear. The gear assembly should slide sideways on the shaft but was stuck in one place. Took the shaft out and there was old looking grease but the grease hole in the shaft was not flowing the new grease. Cleaned up the shaft and inside of gear and removed bushings. The wear on the shaft was not nearly as bad as the OP's shaft. Bushings were like new but I replaced them anyway. The shaft seemed to be worn on the underside (closer to drive axle) so turned it 180 degrees and re-installed. The gear and chainring assembly can now slide sideways on the shaft as expected. Ordered a new shaft and more bushings.

Checked the drive axle and the short axle would not easily pull out from the long axle, and was not fully seated. The long axle was quite corroded where the short axle fits. Cleaned both axles and greased them. Lubricated the chains and gears. Axle and track subframe bearings were good. Reassembled the axles and greased hubs, and the axle can now move sideways for proper alignment. Reassembled the Tracks and all seems well, quieter AutoTurn.

Bought a new idler shaft and bushings for replacement next spring. Quite surprising for a 2 year old machine with only 126 hours on it.

The gear on the shaft can't slide sideways as it is sandwiched between the locking pin that goes through the shaft and the side of the case.
Also the shaft can't be rotated as it fits in the D shaped cut out in the case.
Your machine could be different than this one.

 

Update
After looking at some different models I may have a solution.
It seems that the pinion shaft for Model 921326 (28 Deluxe Trac Drive) is a hardened shaft.
When comparing the two models, that seems to be the only difference.