I must say maybe we are lucky but we have never had a hydro failure of any kind. Our old lazer is still all original and now has 3000 hours on it and in those 3000 hours I hate to admit this but it has had the hydros serviced twice. Now I will say that I strictly use amsoil 20W-50 which uses the best group IV and V synthetic base stocks money can buy and it is also very high in ZDDP which is one of the best anti wear additives you can get for a high sheer application. Group IV and V base stocks do not break down nearly as easy as fake group III fake synthetic oils such as mobil 1. For me the last thing I would be worried about is the hydro system. Overall durability, cut quality and dealer support are my 3 main things I look at when purchasing a mower.