Granville's Strut Seal - Or Other Strut Maintenance Techniques

When I stepped on the wing of my Cherokee 235 today, the strut went
completely flat. I got underneath the wing and lifted the plane back
up to a normal strut position where it stayed until I put any weight
on it; again it went completely flat. I pushed it back up one more
time and put my air gauge on it. I measured 200 psi in the strut so I
assumed the lower o-ring went bad and I needed to get a strut seal
kit. Again I put weight on the strut and it flopped right back down
to bottoming out against the landing gear.

While looking for the parts on line I came across Granvilles' Strut
Seal. I have never heard of this and am wondering if anyone has had
any experience with it. Also welcome is any other input you may have
regarding Piper main gear struts and replacement of the o-rings, or
other workarounds available to avoid needing to replace them.

When I extended the strut after collapse I did notice a small amount
of fluid on the oleo which is leading me to believe the lower end went
bad. The only thing that confuses me is how there could be such a
high air pressure in the strut if it could completely collapse.
Wouldn't the air/nitrogen escape out of the strut as well?

TIA for any responses.
z