Hotpoint FFA90 fridge warm – seal problem?

Have a Hotpoint FFA90P which is roughly 8 years old. In the first year the fridge was getting warm. Called in the service engineer who removed the back panel in the freezer compartment and removed any built up of ice. He repositioned the bottom sensor/thermisister (don’t know what it is called) so it point downwards. He told me that ice builds up around the fan and prevents the cold air going into the fridge.

Since then the fridge does warm up after 5 or 6 months and i then have to go through the hassle of removing the back panel, remove any build up of ice, clean up and replace the panel. The fridge then works perfectly. It is okay for another 5 or 6 months.

Any idea if there is a one-off fix for this? Hate the hassle of doing this. Have noticed that the foam seal around the fan and panel has seen better days. Is there a kit to replace this?

When things are quiet you can hear loud thud from the fridge/freezer. have been told that this is the ice dropping off the elements etc. Also been told that the seal on the door may be faulty allowing warm air in which causes the build up of ice!!!!!

Any advice?

Thanks