Major service at 20K query

[Grumpy Goat]

My bike has reached 20k KM and is due for a major service. As it is still under warranty I thought I would schedule an appointment.
...
But I was wondering if this is common practice? Has anyone required or been charged for a head cover gasket while under warranty?

This is not a common practice and is the first I have ever heard of this. Did the adviser see the bike before making this addition to the estimate, and if so was there oil weeping from the valve cover gasket?

I have had my valve covers off more than once (OK maybe 3 times) and the neoprene (?) gaskets are in perfect condition after 41k miles.

Don't get annoyed; just don't pay to have them replaced. If he wants to replace them he can pay for them.