Electrolux EOU63102X Causing RCD Trip

I have an Electrolux EOU63102X double oven, a while back when we turned on the fan oven it caused the house RCD to trip and knock the electric off. I replaced the fan element and all was good. The old element was visibly broken (the insulation had ruptured over some of the element’s length). Now the oven has started tripping the RCD when turning on the grill in the bottom oven. I assumed the grill element had gone too, the oven is about 12 years old and the fan element had died a while back so it seemed reasonable. I bought a replacement and fitted it. However the RCD still trips when the grill is selected, this is the symbol with just a grill on it. But if I select the symbol with the grill and a line above it which I believe also turns on the element at the top of the oven with the grill, then the grill heats up just fine! When I realised this I also noted I could not see any insulation damage on the grill element I removed. I suspect there is nothing wrong with the element I removed, and perhaps it is the oven selector switch that is shorting something on the grill setting? Am I barking up the wrong tree? How might I check if this is the case? Thanks for your help, apologies for the long post …