Original Eames RAR rocker base?  

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Black bolts? Are they not usually zinc in such a combination as this? Do they seem original? If there is evidence that a chair such as this has been taken apart, I will always assume a marriage has taken place.
(Tell me you're not asking about this to commit evil acts... Counterfeiters please die...)

. . .
Definitely not trying to counterfeit. I'm becoming somewhat of a mid century nerd. I buy some items to have for myself, and some I end up selling. I'm considering purchasing this chair, which is advertised as an original base, but the dealer doesn't strike me as being particularly knowledgeable about the chair so I wanted to verify.
I'm attaching a close up of the shock mount.

lots to consider here
Not very common that you see a rope chair with the red Venice label. Usually the red labels are found on the second generation "no rope" shells. But that is a big PLUS in my opinion, just because this might be my first "live" viewing of this combination.
The base gets a little bit dodgy however. I notice that on the first photo, the mounting tabs on the front appear to have early double rounded ends, which would make it a very early and rare rocker base. But the close up tab is squared off, which suggests a possible replacement of the tab, in addition to the more obvious re weld.
The runners look early and good enough, but it has been repaired somewhere along the line, so that does also raise the question of replacement parts or a marriage of parts. I agree with object worship about the bolts too.
Just from these photos alone, I am guessing its an original but repaired base with a replaced tab or two.
The best part for me is that rope shell and red Venice label combo though!

So, Eameshead, your best...
So, Eameshead, your best guess is that it's at least a Herman Miller runner, and not a subsequent reproduction? What makes you think it's "original," even if a married original?

Tabs
Also, the tabs are all square. They just look a bit rounded off in that photo, but you are actually seeing a piece of the shock mount underneath.

Oh damn
You are right, tabs are not rounded. My mistake.
That makes more sense now, since the rope shell has a later venice label
So now I am far less sure about all aspects of the base and runners, as my whole take on it was because of the tabs! I can't really say anything at all for sure about the base now, except that it is repaired. It may indeed be a repro.
That shell is a great find in itself if it is in good shape though!
Sorry for the error.

Thanks
Thanks eameshead.
Can you drop a little knowledge on me? Would authentic original bases not have that sloppy welding work? Is that what gives you pause?
Are rounded tabs earlier than squared off tabs? Do squared off tabs even exist?
There appear to be no other indentations in the rubber shock mounts.

Tabs
Could have broken off and were repaired and/or replaced at some point.

Woodywood....
Does the rest of the base look right to you? Why or why not?

yes
The sloppy weld was definitely the quick giveaway. Eames bases have very clean and economical welds (if they have not been repaired).
Most all of the rocker bases have four tabs that have one curved edge and one squared off edge.
RE the tabs: I was thinking I saw a double rounded tab on your rocker base.
(And I recalled that with my cats cradle bases, only the very first year bases from 1950 had tabs that were all rounded on BOTH ends)
So when I saw what I thought were the same double rounded tabs on your rocker, I forgot that it was the cats cradle that I was recalling.
It may be that the very earliest and rare "cross strut" rocker base from 49-50 also has the double rounded tabs that are on that cats cradle. (I think it does) But that is not the base you have, and I am sure about that.
Hope this helps! I know many here know more than i do on the rockers, but I was here so,,,
PS Re lack of shock mount indentations: It is quite plausible that the original base was not in solid contact with the shock mounts, especially if the chair got light use. I have seen many older large mounts on various bases that had no sign of imprints. So your mounts are probably original, in case you wondered.

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I'm not seeing indication of a repair in the close-up, it all looks pretty clean... the vintage stuff can actually be quite sloppy, especially on undersides. This has been noted around here before.
It seems like a duck to me, but I haven't seen enough examples of all the vintages to be definitive... The base does look just like the one I just got (that is a later chair). I'd say it's vintage Herman Miller, and even if I couldn't 100% say ORIGINAL vintage I really don't see any red flags and I'd probably go ahead and snatch it...
That is, if in person the base has consistent age-appropriate wear, and it looks like it hasn't ever been taken apart, and it all feels good to you.
Tabs breaking off really seems unlikely.

its so clean
Im all over the map on this.
Objectworship's weld comment is making the weld look less and less sloppy the longer I stare at it.
The zinc base is just so damned clean, and the runners are too.
I could still be convinced that this is vintage, but the zinc coating and the runners just feel too new. It is in awesome condition if it is original.

Definitely a sloppy weld and atypical screws...
Odd example. It could be a hodge podge piece in great condition. But if so, why would there be any need for base repair in that condition? Or perhaps it's a marriage... and perhaps a counterfeit base. Hard to say from those photos...

Thanks lunchbox
Is there a different angle which would help you determine?