Who was the US military pilot who crashed his plane and was accused of selling it to the Russians?
According to the relevant Wikipedia page Lt. David Steeves of the USAF bailed out of a T-33 trainer in 1957 near King's Canyon National Park in California and was not found until 52 days later.  When the crash site could not be located Steeves became the subject of various rumors, despite the T-33 being a relatively unimpressive trainer aircraft.

Steeves left the air force after the incident and reportedly conducted some of his own searches on the ground and in the air before being killed in an unrelated crash in Idaho in 1965.

A canopy located in the park in 1977 was as identified as being from this aircraft in 1978 but the remainder has not been found.  While no developments appear to have taken place in the story since then, it has occasionally been the subject of articles over the years.