Not sure what you mean. Below is a link to my exact product. Maybe you can point an arrow to what you're referring to, so i can get a grasp of what you mean.

I.E. you spoke of a "hose outlet" on my spout??

https://www.americanstandard-us.com/products/slip-on-diverter-tub-spout?variant=43622375456815

Sorry about the confusion. I meant the fitting on the tub spout where the shower hose connects. Unscrew the hose from that fitting, run water through the spout, and if water still comes out of the hose fitting, the diverter is not sealing and that is your culprit.

The 8" x 2" Black Thermoplastic Rubber (TPR) Wheel can be sized for 3/8" (0.375") axle. But with the roller bearing, the total cost would be $25/wheel and the wheel would be slightly smaller than one on the other side of the cart. After 30 years, perhaps it's time to buy a new cart. Amazon has ones that cost $40.

Forget big box stores. They only carry wheels to fit their products and maybe some fast sellers. Harbor Freight might have what you need, but as I said, you will have better success if you walk in with your cart and wheels.

Grainger and the like usually have great websites where you can shop and order what you need, or the website linked by wdccruise also seems great, if you know in advance the exact diameter of the axle, diameter of the wheel and also its thickness. You can always go thinner and use washers to bridge the gap, but usually not the other way around. Good luck!

Please take a picture of the end of the shaft, the part that holds the wheel in place, and we will be able to help you take the wheel off.