Order them all from Weber at one time for the combined $7 shipping. IIRC, I think I've seen people talking about replacement casters at Home Depot that are better and/or cost less. AS for the split in the tube, can you show a pic or give more of a description ? I say that because the end of the tube (the part in the bowl) is designed with a slit.
Also, the newer style lid bale might be of interest to you. When you lift the lid back with the current bale, it tilts over the grill just a bit. With the new style bale, the lid sits all the way back in a vertical position and is out of the way.