I’m gonna say that The Spikes Gang (1974) was the last true Western that Lee Marvin made.
A pretty good little film that never got it’s due. Certainly worth a see.
Director Richard Fleistcher's message is loud and clear: a badguy is not a hero (even if he is a Movie Star) and there is no glory - or freedom - in being a crook. And who better to deliver that message than Lee Marvin?
A great little cast - Gary Grimes, Charles Martin Smith, Marvin, Ron Howard - including two sweet cameo supporting roles by (Western Great) Arthur Hunnicutt and Noah Beery Jr.
Paint Your Wagon (1969) may qualify as having Western flavour ... and Clint Eastwood. But it's a musical. (Yet ... so was Cat Ballou ... in part) I think it’s a pretty good movie in it's own right - and many folks like it, but ... I don't categorize it as a Western.
Survey says ... ?? Your opinion ?
Death Hunt (1981). It has action, guns and horses ... and Charles Bronson. But a Western? I don't feel it.
Others may challenge these judgements. My opinion is not final on anything.