Looks like i have 2 more cents... I would not offer less for a refinished one. I woulds just pay a lot more for one with the original patina. A civvie refinishing, from this purists point of view, is about as desirable as if you chromed it...
The subject of resale value is largely moot, as "resale" is unlikely in the near-term. With a grand total of three 12(3) CA C1 SMGs in private hands in Canada, I don't think that Koldt, Mark36Hamon, or myself are looking to sell in the short term. But let's make believe for a minute. If one of us did decide to sell, and it happened to be a "refinished" example of the three? Just how would that fetch "less" than a non-refinished version? Can someone give me the "book value" of an "original" versus "refinished" 12(3) CA C1 SMG on the Canadian collector's market? Nope - you can't. Because there is no such book value. It is entirely a matter of what the Canadian Militaria collector with the requisite status and the deepest pockets would be willing to pay.
Aside from the above, just how would the "milsurp purists" determine that a gun with 30 years of "military assistance sales" service in Zaire hadn't been previously refinished overseas? I would be willing to bet that none of the three C1 SMGs in private Canadian hands bear their original C.A.L. factory parkerizing. So what is the difference if they are subjected to yet another professional parkerizing? Would a Canadian militaria collector assign a premium to the fact that Koldt's SMG's finish is scarred/worn/rusted as a result of the weapon's diffident use by African (vice Canadian) forces? Who really cares? At the end of the day, the C1 SMGs "are what they are". Most in-service weapons were refinished multiple times. Knowing that, I would ask how a less than perfect finish arising from 1960s use/abuse by the Zaire Army somehow confers "special status" upon a basic C1 SMG. Sorry, but I'm simply not seeing it. I'd much rather have a pristine example that appears to have undergone refinishing at No 3 Workshop in Montreal - as most C1 SMGs did during their life-cycle. Heck - If we weren't talking about this subject honestly, and if the subject of the discussion weren't 3 of a kind, nobody would know the difference.
At the end of the day, how is a "civvie re-parkerizing" any different than a "couldn't give a crap" arsenal refinishing by No 3 Workshop. Same prep, same chemicals, same result.
plus, you say there are only 3 on the registry? the fact yours is the only un-refinished one should make it even rarer(ummm, unique) and thus more valuable as a fuction of its rarity. One day, someone will curse you for the extinction of the last truly original...