Advice on 206 gti please?

I am thinking about buying this 206 gti, im doing a deal with my ford puma, the thing is my dad checked it over last night, and he thinks it has a oil leak, maybe something little which is causing this, or it maybe a big job. The cambelt needs doing, which Its just part of a cars life it has to be done, its done 120k, what is the average miles a 2 litre gti can do? I just dont want to buy it and it plays up on me constantly. I so badly want this car but need some advice on what to do??