You've probably fixed by now but I searched TBN a week ago for this and had a hard time finding much on size of o-ring.
If anyone knows where to find the o-ring sizes hope they'll post it.
I just fixed a 1/4inch loader QC last week.
There was an o-ring in the female QC that was broken. There are two types of seals in mine, the "plastic" one was ok, if it had been bad I probably couldn't have fixed it without OEM parts. Local dealer and TSC didn't have correct QC's in stock so rather than order online and wait I figured I would try matching the o-ring.
It is a bit tricky to get out. I took the connect off the machine and indoors under good light and used plastic toothpicks to get it out.
Took the seal to ACE Hardware, matched up the size...it works. Haven't done any real extended time periods but I lifted the front end off the ground many times to check it and its fine. I was unable to find the exact size o-ring specification on the Snap-Tite website, but got lucky I suppose with matching by eye because part of it was actually missing.
The usual warning....if it doesn't work and were to blow out with anyone under the loader...well..........don't go under the loader or under the machine lifted by the loader without jack stands.
Mine has these on it:
72 Series