Matt,

I have had the same experience trying to find TW, coulters etc. in the field. You would think you could find a shiney 16" coulter...

One pointer, those TW bolts need to be tight. We also have found the HD spring lockwasher we formerly used would spread on impact with a rock, etc and now use a hard 5/8" Grade 8 SAE sized flat washer under the head of the cap screws holding our Trashwheel hubs to the stem base.  This solves many loosening problems. Most of the time when coming off they were just not tightened fully at installation the first time. 

When you have the planter in the shop over the winter maybe change the lock washers for flat washers. Just use a socket and driver drill to unscrew the stems right out of the mounts and do the change with the stem clamped in a vise. Use some never sieze on the cap screws. Loctite doesn't help in this situation.

The hard flat washer helps a lot. Grease them until you see grease coming out around the seal and you should be good to go.

Jim at Dawn