Bosch kim29473gb01 fridge part not cooling effectively

Hi,
Bosch fridge freezer integrated model kim29473/gb01. I’m guessing it’s just over 10years old…

The fridge part no longer seems to be cooling effectively – top part of fridge is warm. Thermostat set to 2 and is constantly flashing.

I’ve replaced the door seal and done a 48hr defrost. On switching back on fridge initially cooled to about zero. But after 12hrs on is back to feeling warm.

I’m stuck now as to what to try next or if given the age we are at replacement fridge time? I’ve seen other posts around a faulty thermostat – is that likely and is it easy to replace? Is it worth calling engineer out?

Advice gratefully received…

Thanks in advance!