I think someone goofed with the weld on the first wheels. That is a very high-torque area and I'm glad to hear that the weld has been beefed up. What size tire is on your tiller?
Be sure to check the air pressure in the tires before using the tiller. If you apply torque to an under-inflated tire it could cause the tire to spin/slip on the wheel. If this happens it can cause the tube to spin with the tire and pull the valve stem inside the tire. When that happens you can't reach the valve stem to add air and about the only option is to stick something with a sharp point into the valve stem hole and puncture the tube so the tire can be completely deflated and repaired. One thing you can do to prevent the valve stem from disappearing into the tire is to find an appropriated sized metal nut and screw down onto the rubber stem, this will usually stop the stem from being pulled inside the tire but it can also cause the valve stem to be ripped off of the tube is there is excessive tire slippage on the wheel. The best insurance is to check the pressure before use and if it's really low (or flat) to have it repaired. Tubes work ok in this type of equipment but they do require the operator to monitor the pressure. Matter of fact, in some situations tubes can be better in that grit and dirt won't get into the bead area and cause slow leaks if the tire is tubeless. Unless you run over a nail or puncture the tire in some way, the tube will work fine with proper air pressure. If you do get a nail in the tire it will need to be broken down and repaired...tire will need to be patched if the hole is big and the tube will need patching or replacing...you can't simply put a repair plug in a tire with a tube in it...
Btw, tire sealants don't work well in situations where a tube is used...they may appear to work for a while, but sealants are intended for tubeless tires....also, some of the sealants are intended for temporary use and can actually corrode the inside of the wheels. Tires with sealants used in them also pose repair problems.
The chemicals used are very "slick" with some of the chemicals are almost impossible to clean. Even with the repair area being cleaned with a solvent and buffed down, the chemical residue can still cause the patch to not adhere well in some instances. Tire sealants are good for emergency auto use when there's no other option or for non-highway tires that are subject to repeat punctures...but these tires have to be tubeless tires for the sealant to work well.
FWIW.
