Injectors

Hi,
I'm after a bit of info.
Will Mk2 Injectors fit the Mk1 and if so, will they run ok?
They look physically the same, but they seem to have an extra rubber o ring near the tip, what is this?

They're on ebay, the description says they'll fit, but i wanted conformation from people in the know (that's you)

Hope you can help
Cheers

I've used Mk2 injectors with the little 'hat' as I have what appears to be the later seats with the plastic lower shroud…….

see Injector Test