UPDATE: Two noted Marx authorities have chimed in, one saw no problem with the gold color and the other declared "Either Marx or Plastimarx" without hesitation. Good enough for me, and if the latter it'd be the first Plastimarx item in my stash.
Factors to consider:
1) Gold is not one of the described original colors.
2) Gold is not one of the described recast colors.
3) Wear, aging and dust consistent with a vintage figure which has been on display.
4) Helmet has slight discoloration consistent with having been on display.
5) Wearing down of the front helmet notch consistent with described originals.
6) The flashing of overspill plastic at the mold seams is more pronounced on the recast.
7) The gold figure has the correct notches on the bottom of his feet consistent with Marx figures.
8) The vendor was an estate specialist, had a nice selection of other confirmed vintage spacemen.
If it is a copy it's likely "vintage" as well: He stood on someone's shelf long enough to collect dust and for the helmet to be slightly yellowed by pollutants. What I would ask is, if it's a bootleg why would it have the notches on the bottom of his feet?
Figure cast in a very soft semi-translucent gold plastic with an interesting marbling swirl. Which does remind me of the marbling on a known Hong Kong copy of an Ajax female also cast in a soft semi-translucent plastic but was significantly altered from the original pose. This is either an original, an exact copy of a Marx figure, or was cast in the same molds as the Mexican recasts by someone other than Marx before the Mexican figures were made.
With known Mexican recast from the 1990s at right. The recasts are only described as being cast in a "smoky metallic silver". By my eyes the gold figure is also "older" in the sense that it was somebody's toy, played with for many years before coming into the hands of a collector.
Described original figures cast in metallic blue, metallic green, silver and white. Though the reference source cited their size as 5 inches. If they got that wrong ... Counter point is that I have metallic blue, green and silver figures of the 70mm "Rex Mars Official Planet Patrol" figures released prior to these and their plastic is less waxy and stiffer than this gold stuff.
Note wear to helmet notch, a described trait of the original figures due to the softness of the plastic. The Mexican recasts use a much stiffer plastic and my recast example was new/unused. This was played with extensively.
Known Mexican recast helmet at right.
Left: Semi translucent light absorbing plastic.
Right: Opaque light reflecting plastic.
The seam overspill / flashing is much more pronounced on the Mexican recast.
Note the difference in the hands.
Better trimming to the gold figure. The thumb on the gold figure also appears to be further away and better defined than the thumb on the silver recast.
Pictures are helpful but are only a representation of the figure.
Do I think it's a Marx original? Unsure just what to think.
Do I hope it's a Marx original? Not any more, though I did at first. Man enough to admit that.
My collecting motto runs "You buy the spaceman and not the story." No claim was made about the gold figure other than it was vintage so nobody got had however it may work out. The price was very reasonable and it's different enough from the recast to be of interest regardless of what it's story might be. In terms of probability my call is a 60% chance that it was not made by Marx and likely to remain an unknown. Only thing which can be said for sure is that he's cast in a very different plastic than the Mexican re-issue and has been around much longer than they have. He was somebody's toy once until ending up in an estate liquidation. Now it's my turn to have him, and someday he'll pass along to another enthusiast at my estate liquidation. We just rent these things for a while.
