10+ year old Neff oven, just decided to trip RCD, no previous trouble.

99% of the time it's used in fan mode (where the element used is within
the fan).

Just went to use it in a different mode where top and bottom elements
used, but not fan, it had been heating up for a couple of minutes then
tripped the RCD in its half of the CU.

Hoped it was a one-off, so reset and tried again, tripped again,
wondered if the internal light was causing it so removed bulb, still
tripped.

Each time after resetting RCD have to prod the timer button to "ack" the
mains failure, then the electronics are on (i.e. clock flashes) if the
main selector knob is "off", it doesn't trip.

If I turn temperature knob to coldest, I can turn the selector knob to
the setting where just the internal light is on, it doesn't trip (a
small cooling fan also runs)

Leaving selector knob in the internal light setting (i.e. no elements or
main fan) then turning up the temperature knob it trips the RCD as soon
as I hear the stat click on.

To me that doesn't scream "earth leaky element" but rather "gunge has
got into stat or across some wiring"

Thoughts?