Sly, that is, not Frank.
IMDB shows a Rambo movie that I’ve never heard of.
First Blood 1982
Rambo–First Blood II 1985
Rambo III 1988
I’ve never heard of that third movie. And the plot summary is definitely not any of the other three.
IMBD also has no details on cast other than SS, also.
So, it’s either a lost masterpiece in the Rambo series, or it’s a wild goose chase.