I am trying to replace the seal behind the front sprocket on my nc30, got the front sprocket off ,but cant seem to figure out how to get the old seal out any tips pleasw

Not easy without splitting the engine cases. The old seal can be removed with screw driver and hammer, rough but effective. New seal installation is the big issue. There is a ridge on the outer surface of the seal that sits in a groove in the cases. Maybe a press can push the seal home.

I'd always thought this was a bigger job than it looked - this is the output seal isn't it?

I don't think it goes in form the outside - have a look at the service manual and find out what that says.

And welcome Andy...it's the place to find out the answers

I always thought it was a engine out/split cases