A piece of advice for anyone thinking of changing stem seals in a MK3 Astra.
I have just change 16 of them having of course a 16v. Now I bought a FAI head gasket set the thing is the stem seals in it were not that good some stayed down most came back up. Using a soft piece of pipe on too the stem seals thinking the palm of my hand knocking the pipe twice would put them in to place. Thing is it did not I had to use a rubber mallet as they were tight which of course being tight made them pop back up something to do with the tightness pushing them back up. So I decided to get Vauxhall stem seals to correct this which are fine two bangs on the tube with the palm of my hand they went in to place not tight and the correct fit. So avoid using the stem seals in a FAI head gasket set or any other non Vauxhall head gasket set use Vauxhall ones. One other piece of advice make sure before starting out taking the car apart to get the head off make sure you have TORX sockets I played safe and bought set of sixteen sockets as that covers more sizes knowing my luck if I had bought a small set the socket I would have wanted wouldn't have been in it. You only get the sockets nothing else. I got mine of the internet as Halfords set was smaller and cost around the same.
Set of 16 stem seals from a dealership will cost you plus VAT £25. I would do what it did check ebay as well. I found some Vauxhall stem seals still sealed in the orginal GM bag right part number (number on the bag is - 90410741) for 99p with no bids, which was the price I got them for saving me £24.01 so worth checking out ebay before you try a dealership.
I hope all this has been some help to you all.