Hi Derk,
Just been catching up with your thread.
About your Grease Gun, I don't think that either are correct for your GPW. I had a thread on the G503 about a GG that i have, this is it,
http://g503.com/forums/viewtopic.php?f=48&t=272329
It may give you an insight. I have just bought another GG with bakelite handle that's not correct either
Keep up the good work,
Dave