Smearing "ammo with human feces" sounds a bit odd as well.Hadn't heard of that one before.
American lower rank prisoners were taken in the ground fighting in the south.For example the 3/3 Marines had Lance Corporal Leonard R.Budd captured near the DMZ in August 1967,released in 1973.
http://www.chadduck.com/ymarines/pow-mia/bios/b115.htm
PFC William Baird of the 196th Brigade was also captured near the DMZ in 1968,released in 1973:
http://www.pownetwork.org/bios/b/b007.htm
PeterBaird was assigned as an infantryman with the 196th Light Infantry Brigade
of the Americal Division. He took part in patrols, search and destroy
missions, guard duty, and fought in the Tet Offensive in March 1968.
About 3:00 PM on the afternoon of May 6, 1968, thirty men of Baird's company
went out on patrol. They were close to the de-militarized zone on the
border of North Vietnam. Bill was pointman and a good 20 feet ahead of the
rest of the men. They had no idea they were walking into an ambush. While
walking on top of a dike in a rice paddy, Bill stepped on a land mine. The
explosion not only rendered him unconscious, it also alerted the Viet Cong
and a firefight broke out.
Three hours later Baird regained consciousness and heard the action going
on. Men were yelling, screaming, and shooting. An artillery barrage was
going on and planes were overhead. Bill began to take stock of where he was
and realized he must have stepped on a mine. There was no one near to help
him. He tried to stand up but discovered he had no feeling from the waist
down and through his efforts he passed out again.
As darkness approached things quieted down but Bill suffered the trauma of
being wounded and left alone. Eventually he heard the voices of Vietnamese
approaching. He had no idea if they were friendly or not. Then as they
came upon him he heard, "Chu Hoi"', surrender or die.
The Vietnamese surrounded Baird and when he told them he was injured they
did not believe him. They told him, "Americans are sneaky, lie, and can not
be trusted." Several times they tried to make him stand but he could not.
He then felt a sharp pain and a ringing in his head and discovered that they
had shot him. Fortunately the bullet hit no vital point, entering his neck
and exiting out his ear.
Finally convinced that Baird could not walk, the Vietnamese made a makeshift
stretcher and drug him along with them. After dragging him for three or
four hours they stopped and gave him a bowl of rice. Traveling to the north
they proceeded to show him off at all the villages they passed through and
the people would kick and spit at him. This went on for most of a month.