400: 400 S2 Freezer Sensor problem

[thepenn]

Apparently the thermostat and sensor on my chest freezer needs replacing, the problem is the location of the sensor. It is located level with the evaporator coils with no access. The freezer body is surrounded by fitted Alpi wood, fitted at the factory; access is only available to the compressor assembly underneath the freezer and the thermostat assembly just inside, top left. A refrigeration engineer has already checked all other components which are ok.
When a problem developed when under warranty, an engineer fitted a new thermostat; what I did not know is that he had the same problem and fitted the sensor lead at the top of the freezer which made it 'apparently work, but food at the bottom was not freezing, this was combined with language issues.

Has anyone had a similar problem? Alternatively, I would be grateful for any workable solutions.