It's a HW110 not HW100

Don you made me look and i found this as you might have 

https://www.tapatalk.com/groups/weihrauchowners/a-definative-o-ring-list-t3775.html

a quick measure on the stem will tell you, it should be 3mm with the cross section at 1.5mm times 2 equals an OD of 6mm 

http://www.airgunspares.com/store/product/9817/WEIHRAUCH-HW100-Valve-Stem-Seal-PTFE-Part-No.-2655D/

so they are a teflon o-ring and the O-ring Store doesn't have them in that size 

you can find all the o-ring as kits on Ebay from the UK or your choice 

and i have never owned a HW 100 i just looked around for my Sunday learning lesson 

good luck and take care

mike

Yes, thats where l found the size. Just trying to verify this is right.

I don't have the gun yet. Don

Just rebuilt mine for the season got the o-ring set off of ebay and a regulator test gage from HW100tuning .com

You can everything from them if to want shipping was very quick.

Well, a friend pointed out the gun l'm getting is a HW110 and not a 100. The gun is listed as having a "built in air tube" so thinking you can't just screw it off like the HW100. It was bough with the understanding that the fill valve is leaking so not sure if gauge/ fill valve will screw off on 110 like a 100. Don

I took a look at couple of my HW100s and my HW110 and my guess is that (after degassed) the manometer unscrews from the end of the air cylinder were you can access the check valve if its leaking from that end. I would think using a dowel into the filler probe hole to unscrew it would be the simplist way to do it. It is my understanding that the HW100 and HW110 share the same air cylinder and it looks that way comparing several of mine here but I am unsure if it unscrews from the receiver like the HW100s do.

Saw a video review on the UK spec sub 12fpe 177 and boy was it REALLY QUIET and 120 shots per 200 BAR fill! He was plinking at 100 yards!

HA