Which Oil? - Advice needed!

[speedynz]

You need 4.7 litres (including filling the filter), I've just paid 65 pounds for 5 litres.

If you do change it you should (at the very least) drain the existing filter housing (easy, but you need a 36mm socket) so as to avoid cross contamination with the existing oil.

[Smythe1981]

the annoying thing is since i've had the car i've topped it up with about 2 litres of Castrol as recommended on here and by the stickers on the car

but i'm thinking now, what if they had previously put shell in at the garage when i bought the car and i've since put castrol in, which isn't recommended mixing oils

what sort of damage are we talking about?

havent noticed any performance drop, still goes as sweet as it did on day 1