AEG Competence 4101-4 Not Reaching Correct Temperature

I noticed today that the oven took forever to heat up and still did not reach the correct temperature. It was set at 200C fan but only managed to reach 160C according to my separate manual oven thermometer. This tallied with my turning the temperature knob down until the light went out. It was on bottom heat option. I tried it on normal fan and it heated for a while and the temperature light went off but my thermometer still said 160C. I tried it on normal (non fan) heating and it reached 180C but still only registering 160C on the temperature knob.

Is this an element that has failed or a thermostat or something else? The oven is knocking on a bit now, 11 years old, and I’m wondering whether a repair is a good or bad idea.