Joe, your rheostat may be rebuildable- by you- in minutes. First remove the thing from the dash. Inside the assembly is a hair-fine wire that unaccountably carries all the current thru the assembly. It cracks with age/vibration. On the back of the unit are two large copper stubs that protrude thru the bakelite plastic- maybe test points. Solder a very short jumper wire between the stubs and likely the rheostat will work again.
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