If you use it with extreme care and not regularly it will not damage the leather. I carefully clean my leather steering wheel about every 36 months and protect it afterwards using a preservative (matt finish) I got from a local leather retrimmer.
I currently have a leather MK3 ST steering wheel which was in pretty bad condition. The previous owner used a gloss preservative on the leather and the stitches were molded because the car was exposed to the elements after an accident. After cleaning and preserving the leather the steering wheel is back in mint condition.
I use a melamine foam sponge to clean a leather steering wheel. The melamine foam removes all kind of contamination including skin greases without any problem. During time most leather steering wheels become shiny as a result of contamination and skin greases. After cleaning the steering wheel with the melamine foam sponge the steering wheel has again the original matt finish.
A degreaser can dissolve/soften the coloured top layer of the leather. If this is the case the best option to solve this will be another steering wheel. These days a used mint condition leather steering wheel can be found for little money.
A focus mk1/mk1.5 Ghia did have a real leather steering wheel. The lower spec mk1/mk1.5 versions did have a plastic or artificial leather steering wheel. The artificial leather steering wheels are known to become sticky during time or if not being treated correctly. In some cases the coloured top layer of the artificial leather may even peel off.
If your car still has the original Ghia steering wheel it should be real leather.