Yes, over time they lose efficiency.
What I'm trying to find is the instruction manual so you can check the thermostat setting.
The higher the number, the colder it gets.
An overall service, sorry, there's no such thing.
You'd be looking at a new compressor and regas, circa £200 to get it cooling again, if it's the system at fault.
If it's the thermostat cutting out too early then you'd be looking at a less expensive repair.
Unfortunately, I can only say a thermostat will cost between £30 and £100 (depending on the one fitted to your model).
Given the age of your appliance, I would suggest replacing it.
Even if you spend the £200 or so, everything else about the machine would still be old.
Hope this helps