Acceptable amount of corrosion/discoloration

[rsingler]

Balance shaft is a bit misleading as a part name for this reg. Since the design is downstream, the "balance" items really just serve to add light second spring tension to the back of the poppet.
The oring just serves as a seal to keep the reg from breathing wet. There is no Intermediate Pressure in this balance mechanism.
To test your repair, just do a negative pressure test with the hose inlet blocked by sucking on the mouthpiece. If you can hear/feel a little leak around the knob mechanism, then try springing for a new balance shaft. If not, you're good to go. If the leak is very tiny, it may not even be worth the effort, since the pressure differential during breathing will be only a couple of inches water column. If the reg breathes dry, you're fine.
When you reassemble for the test, just barely lube the oring for the shaft. Otherwise you can hide the potential leak for awhile.
And as an alternative "repair", you can gob up the balance area with lots of extra thick silicone lube. That'll keep you going for a long time.

 

[Abz]

Balance shaft is a bit misleading as a part name for this reg. Since the design is downstream, the "balance" items really just serve to add light second spring tension to the back of the poppet.
The oring just serves as a seal to keep the reg from breathing wet. There is no Intermediate Pressure in this balance mechanism.
To test your repair, just do a negative pressure test with the hose inlet blocked by sucking on the mouthpiece. If you can hear/feel a little leak around the knob mechanism, then try springing for a new balance shaft. If not, you're good to go. If the leak is very tiny, it may not even be worth the effort, since the pressure differential during breathing will be only a couple of inches water column. If the reg breathes dry, you're fine.
When you reassemble for the test, just barely lube the oring for the shaft. Otherwise you can hide the potential leak for awhile.
And as an alternative "repair", you can gob up the balance area with lots of extra thick silicone lube. That'll keep you going for a long time.

Thank you so much for all of the detailed information! I already did a negative pressure test and it held and I only lubricated the O-ring lightly (using standard silicone lube, I'm sticking to regular air or a maximum of 32% EANx) so it seems like the shaft is holding well so far.
also thank you for clarifying that there is no balancing action going on as I was banging my head trying to figure out how a consistent spring tension is providing balance at the second stage.

Last question, do you know where I can find manufacturer specific O-rings? I found most of the items I need to service reg on aquasportscuba.com but could not find O-rings 2.010 and 2.004 on their website or anywhere else. I can't tell if those O-rings are standard sizes or where to get them from.

 

[halocline]

It's pretty rare that scuba regulators use o-rings that are not standard sizes; keep in mind that there are a few different sizing schemes, including metric.

This is a place I've ordered from:
https://oringsusa.com

There's also mcmaster carr, and parker. And others, I'm sure.

Oops, I see you are not in the U.S. Sorry I can't be more help in your part of the world.

 

[rsingler]

Last question, do you know where I can find manufacturer specific O-rings? I found most of the items I need to service reg on aquasportscuba.com but could not find O-rings 2.010 and 2.004 on their website or anywhere else. I can't tell if those O-rings are standard sizes or where to get them from.

I'll have to look on another Delta in the shop, but from previous experience with Deltas I'd be willing to bet that those two orings are just what their part numbers suggest: AS568 2-010 and 2-004 size. Nitrile Duro 70-75 will work just fine and a bag of 50 is still pretty cheap. Or one of the cheap oring sets online that covers that spread will likely have both. But any material is fine in this location: Buna-N, EPDM or Viton.

I'll open up a Delta and look, but I'm almost sure that's what they are.

If your sources are metric only, those two orings are
2-004 1.78mm C/S x 1.78mm ID
2-010 1.78mm C/S x 6.07mm ID

 

[Abz]

Thank you all so much!