I used to have a Bocanegra - Was a great car and i never had any problems with it apart from high oil consumption.
Very nippy car but in general they are notorious for being so unreliable. Mine drank alot of oil which was 'perfectly normal' according to Seat. Id say it was burning around 1 litre oil per 1000 miles, I just had to keep my eye on it and made sure it never ran dry.
As mentioned above the engines are highly unreliable therefore you'd be daft to own one without warranty. The older engine is the CAVE engine which i'd personally avoid as its the one which is highly unreliable. I'd only get the BOC/Cupra with the CTHE engine as that is the revised better one. SEAT/VW/Skoda changed to these engines after the 2012 cars were released (Dont quote me there, but it was around this time).
Check out the 'Team Boc!' page on facebook. Plenty of information on there