When I started this thread I only got into rebuilding my pump because it was leaking externally. And only replaced those o-rings that were leaking. 11 months later I'm happy to report I haven't had an external leak.
Now internally? In the past 4 weeks I've noticed a shuddering loss of power in the PS Steering system. It doesn't just stop. It pulses. Like when you get air in the system. But there's no air in the system. I looked for the telltale sign of foamy PS/ATF in the tank. Nothing. And the "air in the line" whine is not there. I diagnose it as the internal o-rings finally going bad, and high pressure fluid is slipping past the seals to the low pressure side.
So 11 months later I get to do this again.
Purchased all my parts from McMaster-Carr again. Even ordered the FEP-encapsulated ones again. They're the cheapest ones rated "Excellent" for use in hydraulic fluid and are good up to 400 degrees F. Buna-N are only rated "Good" and are good only to 212 degrees F.
Purchased a high precision bearing from there also.
Here's what the FEP rings look like after 11 months of use. Really. This is a picture of the used rings that have been in there for 11 months.
New bearing pressed on.
New ring. This is the -021 Extra info! Several reports of the -021 O-Ring being too thin on some pumps. The next thickest size with the same inner diameter is -119. Some fellas and I haven't had a problem with the -021. Nevertheless, some other's pumps won't build pressure unless the -119 is used for replacement. So to be safe just get the -119
Here's the new and old -136
The old -136 started life round and soft. Now it's flat and brittle.
Reassembled and working. Just need to get all the air out.