Poseidon Cyklon 300

I just a used Cyklon 300, first stage 2305 old type, and when I turned on
the air, I got bubbles coming out the hp port, I tightened the gauge hose
and that seemed fine, then a few days later when I was gearing up for a
dive, and turned the air on the bc lp hose where it connects starts slowly
leaking. I downloaded the manual and says that instead of o-rings something
called nylon gasket seat was used in the port. Where can I find this part?
I don't have a Poseidon dealer near me but have been told that many parts
are still available for this model.

The water here in TN is still pretty cold so I did not do but a short dive
but when I breathed from the 300 there was a stutter or took quite a bit of
inhalation to get the thing breathing. On the dive, which was very shallow
I had no problems at all, no wet breathing or hard inhalation or any
resistance. Just wondering about this. I had read somewhere that this
regulator, am told this was made in the 1970s was not made for 3000 PSI
tanks and that at the pressure breathes hard, until psi goes down some. In
fact is suppose to get easier to breathe. Anything thing to these?

Thanks,

James