Neff U1721 – advice request

Our Neff U1721 has gone through several elements in the bottom oven since 2004. All apart from the last one have gone open-circuit after varying lenghs of time. More recently the oven started to trip the RCD, only once it gets up to temperature. Given the history of element problems, I took out the element and ran both earth leakage and insulation tests on the element using a Megger tester. The insulation test was fine (approaching infinity on the scale) but a steadily increasing earth leakage current was present as soon as the element started to glow, rising until it was off te scale. I then heated up the element for half an hour, having read about the possibility of moisture in the element, but this made no difference to subsequent test results.

My theory is that since the element is bolted to the back of the oven, this leakage current would find its way out to trip the RCD. However if this is the case, I don’t understand why the RCD trips only once the oven is up to temperature, when the leakage current appears on the Megger tester within under a minute.

Is this enough to condemn the element, or should I be looking elsewhere in the oven? At present I don’t have a known good element to use as a control case. I had hoped to run the element within the oven, but with it not bolted to the back of the oven. I expected this not to trip the RCD. However it proved impractical to set this up.

We checked the temperature of the oven using an oven thermometer, and it was spot-on.

I would appreciate any advice. Apologies for the very long post.