Joker has the best idea! Seriously, automobile insurance companies usually won't honor a vehicle that is not road-worthy for an extended period of time. However, I don't see why your home owners insurance won't cover a loss that is related to theft of your personal property from your yard or garage. Some would say that just leaving it out in a vacant lot for the buzzards would not constitute proper care and guardianship. In other words, a situation created by a property owner as a deliberate invitation for somone to steal something for the intent purpose of recompensation and replacement. I'd talk with my homeowners insurance representitive again if I were you and tell them that the parts are as valuable to you as any of your other personal possessions. Good luck and keep us informed.
