Update: This only worked for 1 day. :-[
I used a parker size 2-110
3/8 I.D. 9/16 O.D. 3/32 C.S.
Actual Size 0.362 I.D. 0.103 C.S.
Looks to be a good fit, as of today its working without leaking.
This is what the materials read as so hopefully it lasts.
Materials
The standard materials supplied with
AS568 Kits and Metric Kits are nitrile
rubber compounds N1470-70 and
N1490-90. N1470-70 is compatible with
most petroleum-based oils, greases,
hydraulic fluids up to 121°C (250°F), as
well as water glycol hydraulic fluid up to
48°C (120°F). N1490-90 is normally
supplied for hydraulic fittings but also
suited for general purpose applications.
For more demanding sealing conditions,
Parker offers a wide variety of polymer
families including
I grabbed it out of a kit our maintenance guy had for other hydraulic machinery. Since it's only for the clutch I don't see testing it as a risk. Im still planning on ordering the kit as a backup. I didn't find the larger o-ring but I measured it something like a .63 .I.D. .890 O.D.
I went by Napa and O'reilly looking for the larger one and they both had what looked to be the same kit.