Nice job!  Always a good day turning something on the lathe.

Condolences, and if you need anything don’t hesitate to post.

The ID of most cylinders is just honed steel tube, not polished & plated like the rod.  The surface that the piston seal rides on isn’t nearly as perfect as the rod seal.  Who knows what concoction of “rubber” was being used at the time to make the seals.  Take it apart and measure it up.  Worst case you put new u-cup seals in them and it still leaks down.  The seals are not costly.  I can’t think of another way it would have failed unless there is contamination / rust inside or if the surface finish of the honed tube is poor.

Maybe replace the oil when you are done just for good measure?

Cylinders are not that bad to work on.  Just make sure you have a safe way of disassembling them.  Don’t use compressed air to make a parts cannon. You don’t want to launch the rod and piston into low earth orbit.   If they can’t be pulled apart by hand once the gland nut is removed rig both ends to something stationary and pull it apart with a come along or chain fall.

U-cup seals (poly-packs) are common.  McMaster Carr (think industrial Amazon but not evil) has them.
https://www.mcmaster.com/products/polypack-lip-seals/

Lots of things it could be, but the seals are most likely.    Could also be that the piston is loose on the rod.

What type of hydraulic oil are you running?

Bob,
I no-showed this year which wasn’t my intention.  Thanks for hosting in California.   I ended up traveling over 1300 miles on the Bash weekend for work and a big trip with my oldest kid.  Honestly the trip with my kid was more of a cannonball run but was productive.

Hopefully I can sneak away to a bash before I get to retirement age.

They can be fussy.  It is easy to push to hard and skip a thread starting them.  Get good lighting, put your good glasses on, get them good and square, push lightly and turn.  For lack of a better description I have had to push sideways on the install tool towards the leading edge of the insert as it starts. 

Maybe run the tap again just in case you malformed anything with the last 4 inserts.

https://youtu.be/wx0v0LWq4ik

Copy- I might drive the Fiesta, or if I am adventurous the 67’ Toyota.

I drove through Bakersfield this past weekend on my way to Huntington Beach.  If I wouldn’t have been in such a hurry I would have reached out.

How was the Bakersfield earthquake?

Facepalm.  So much for QC

Like Death Valley with 3 In-N-Out burger joints.

Add your pics here.  We had a good little show in Yreka CA