Gah. My electric immersion heater went again this weekend. This is the third time in about six years. All three have been heavily corroded, right through to the element, causing short circuit failures. They are a royal PITB to change. Anyway the new one I got says it is “alloy sheathed”. The last three have all been copper sheathed. Is my new immersion heater likely to be made from a nickel alloy? Is it likely to be more or less prone to corrosion failure? Thanks.