Also keep in mind that buying or selling a second hand ML detector, that the warranty is NOT transferable. Many listings on Ebay, especially for 4000's and 4500's will say "it's still under warranty". It's not Caveat Emptor Robert
Some dealers here in Oz are being hounded by Sudanese to put them on coils.I was in one dealer's shop last week when two Sudanese ordered 50 ferrite rings. Even after the dealer told them repeatedly that they don't need them. They replied "We can get a lot more for them with the ferrite ring attached" Robert