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Are you referring to the expansion plug?
Sorry for the delay as well. I was tied up yesterday and didn't have much opportunity to be online.
This is a really basic repair, so I don't think you'll have any problem with it, although it can be a bit messy to deal with the oil. The poppet valve just unscrews (normal RH thread) with a allen wrench (9/16" if I recall correctly). If you are leaking in this location, then most likely you have a damaged o-ring under the head of the valve. Cleanliness is the greatest concern. Make sure there's no foreign material around that can make its way into the cavity once you remove the valve. It will come straight out an the new one goes straight in. Make sure you check the oil level after the repair.
This manual may be helpful as well.