Problem with Scholtes Fridge RF1608

I have a built-In Scholtes fridge freezer, most likely 18 years old. The fridge part has developed a problem, with ice build up at the back/top. A defrost helped but only for a coupe of days until the ice built up again. The fridge is cold but not as cold as it should be.

I’ve rung a couple of repair companies. One said they won’t fix it as its over 15 years old as parts may be unavailable. The other agreed to visit, but I’m concerned that the callout fee will be wasted if the parts issue is correct.

With a freezer of this age and from this non-uk manufacturer, am I wasting my time getting an engineer and should I simply look at replacement options ? I’d prefer to get it fixed if possible.

Anyone know about Scholtes fridges and/or have suggestions on the best way forward ?

Thanks in advance.