Posted for "Christopher Zavatson" <Christopher.Zavatson@udlp.com>:

Rick,
I have seen these washers fail and recommend replacing them if  you
have reason to overhaul the cylinder.  I had one fail catastrophically. Without warning it began leaking so much that the hydraulic pump ran
almost continuously.  After this experience, I replaced the remaining
washers and found another on the verge of failing.  On each, the rubber
had cracked and split around the entire circumference.  The washer that
finally leaked also cracked radially which then provided a leak path. These are standard parts available at McMaster. I don't recall the size
needed for our cylinders, but part #93783A030 will get you close.  Use
Vaseline on the rubber when installing new washers to prevent damage.
Chris Zavatson
N91CZ
L360-std