I have the VAG 1.8 EA888 engine in my Polo GTI - slightly higher power output in the Polo GTI than in the Leon, but I believe it’s essentially the same power plant. I’ve owned the car since new (March 2016) and I’ve had no issues with the engine in that time. The car has only covered just over 20k miles as I only do around 6k miles per year
There was an issue with timing chain tensioners failing on the 2.0 litre version of the previous generation EA888 engine fitted to the mk6 VW Golf GTI (don’t know if this affected Seat models fitted with the same engine?), but not heard of any issues with the gen 3 1.8 fitted to the
mk3 Leon / 6c Polo GTI.
I’m on the time and distance (fixed) service regime and apart from having to add around 200ml of oil in the first year, it’s never needed to be topped up between services since then.
Performance is very good, as is fuel consumption - the long term average mpg is currently showing between 42-43 mpg. My driving is a mix of roughly 20% town driving, 65% single carriageway A and B roads and 15% ‘faster’ roads; dual carriageways / motorways.
I’d check that the service record of the car you’re considering to make sure it has a full service history, and if it’s got DSG transmission, that the DSG service was carried out a 40k miles.