Hi Rick, have you tried taking the temp out of the washer and spraying silicone lubricant into it etc, often you can get these to work again, if you can't replace it with the correct three button switch, they are around.

The agitator [ should ] just lift off but is stuck because it probably has not been removed in about 40 years.

Unless you want a BIG project just leave it in place if it does not come out easily, the mineral build-up etc will either get better or worse depending how you use the washer, but it will not affect the washers performance.

John L.