I'm also interested in the cause of the loss of power. Fuel issues come to mind in this scenario, but this aircraft had fuel and a simple fuel system- a single tank mounted behind the firewall that gravity feeds the carburetor. So it wasn't fuel exhaustion or a pump or tank-switching issue. I found some interesting details on the Ryan posted a few years ago by the owner/restorer/pilot of a PT-22.
https://www.ferrarichat.com/forum/142010793-post8.html
Some of his comments:
"Lots of engine failures and a good majority are from pilots not turning the oil shut off back on before flight." (It has a dry oil sump, and a shut-off valve to keep oil from leaking into the engine while it's sitting.)
"Very pleasant on the controls and not very challenging to fly UNLESS the engine fails. Then it is one of the most serious airplanes out there."