Thanks for the inputNo, but a high quality valve stem is nice to have...........and some of the better built valve stems happen to be metal. Main thing is you want the core to remove easily and thread nicely and sometimes, the metal valve stems seem to "function better", but I wouldn't say its a requirement.
Thanks for the input"Do you have to"....No!!! The question is, are the valve stems that are in your tractor tires now good for both air and liquid. Probably not it the tires were filled with air.
So, yes your valve stems SHOULD be changed to valve stems that are good for liquid and air if you are going to liquid fill your tires. These valve stems will usually be stainless. Now, that doesn't mean your current valve stems will fail. They could!!