Zanussi fridge not cooling sufficiently, freezer OK

Hi,
I have an integrated Zanussi ZBB27450SA. It looks like a typical fridge/freezer, not a frost free.
The fridge is far warmer than it should be, around 10C. Freezer seems to be fine with small amounts of frost.

Steps I have done:
I switched it off to defrost it, which didn’t help.
I bridged the thermostat to make it run all of the time, which brought the fridge down to 0C after a few hours.
I replaced the thermostat with a new one, and now it is back to being too warm. When it is warm, the compressor isn’t running.

A repairman diagnosed this to be low on gas, and not worth repairing. I just want a second opinion before I recycle it.
Any thoughts?

Thanks!
Chris.