Great article. Here are some O Rings that I found I could use for this repair:
A.) The small one used at the base of the vacuum gauge: 3/16” x 5/16” x 1/16” (No.: #008)
B.) The O ring around the front cap: 3/4” x 1” x 1/8” ( No.: #210 )
C.) The O ring around the piston: Not able to find a replacement. Possibly a #211 or a #313 or 3x19 metric?