Smeg SUK61 MFX tripping out

Hi.. hopefully one of the brighter sparks amongst you can help me out…

I have a dual fuel cooker, gas hob and electric fan assisted oven..
the aforementioned smeg SUK61MFX.

Since last week it has been tripping out a lot. It is wired to a 13 amp plug, which normally blows and trips the RCD on the kitchen circuit. The sparky who had a look at it this weekend said that was fine to be wired to a plug , then he replaced one of the spade connectors from the power line connector, but this hasnt made any odds.

It is behaving in a fairly random manner.. in that sometimes comes on and stays on for a while, the oven heats up and the fan spins up, other times it blows the fuse (13amp) as soon as power is applied by resetting the RCD. I doubt its to do with the thermostat as it will blow sometimes when the oven is cold, and the clock seems fine.
But the last time it blew I thought I caught sight of a blue arc near the top element, but it was out the corner of my eye so i couldnt be 100{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} sure.

talked to a cooker engineer tuesday, who said it was possible the element at the top had crapped out or gotten damp, but I dont understand how it could have gotten damp given that the oven is in almost daily use.

my point being, does the element seem likely to be the cause?
I have looked at he element and can see no visible damage.

Cheers in advance for any help.