You are supposed to apply the gasket first and them jam the tip of the glue tube underneath and start squeezing the glue in there.
But it makes a hell of a mess as it drips out. That indentation rides over the rollers, and the last thing I need is big glue bumps in there.
So I put some gloves on, and tip the drum on its side. This is much neater. Was that in teh instructions?
And I clean up my mess.