I suspect I may have found a new lead to the maker of the Oplenflex. After some searching, I thought it looked similar to an Airesflex. However, no Rektor shutter was mentioned for Aires and the lock on the bottom of the camera was distinctly different. The Oplenflex pictured in the article has a lock that was new to me. It's unlike the Rollei locks.

After searching for cameras equipped with a Rektor shutter, I found the Soligor Reflex Semi Auto on TLR This camera has both a Rektor shutter and this curious lock on the bottom marked "Japan", like on the Oplenflex.

My copy of McKeown (10th. ed., p. 400) shows a similar Soligor Reflex with this lock and states that Soligor was a trade name for cameras made by different makers. I strongly suspect the Oplenflex and the Soligor semi automat were made by the same manufacturer.--driesvandenelzen 18:30, 15 February 2008 (EST)

Another obscure but similar camera: the Osiroflex on TLR Notice the sunken flash contact and the Rollei style nameplate, like on the Oplenflex. It has this same bottom lock. Unfortunately, I can't find the OMS company in my copy of McKeown. --driesvandenelzen 18:40, 15 February 2008 (EST)
I think that I got it. I first concentrated on the crank-advance models, and found an advert for an Autoflex crank-advance model distributed by Minagawa together with the postwar First Six and the Pentaflex. The Pentaflex is just another name for the Firstflex-35 and this rang a bell. The advertised Autoflex has a Rektor shutter, and looks the same as the Oplenflex. Two versions were advertised, differing by the presence of a split-image rangefinder in the viewing screen. This Autoflex was certainly made by Tokiwa Seiki, which made the Pentaflex and First Six. This also explains the logo, which can be read as TSK.
Then I found pictures of the Autoflex and of another name variant, the Skymatic, on this page of The cameras look the same as the Oplenflex, and the Skymatic has the same logo. As said in this page, you can check the Autoflex in McKeown, where it is attributed to "Kiyabashi Kogaku", in my opinion a non-existing company and a confusion by McKeown.
The temporary conclusion is that the Oplenflex is a name variant of the Autoflex made by Tokiwa Seiki for an unknown distributor which used the "Oplen" brand, perhaps for export.
--Rebollo fr 05:36, 16 February 2008 (EST)

I found some leads and opened this page discovering you already had resolved the mystery. I had already made a search based on the typical features found on the Rolleiflex copy OPLENFLEX as follows:

1 - Lever wind with hole lower left for knob storage.
2 - Hinge release lever on combined back door hinge/strap bracket.
3 - Placement of frame counter window (revealing type of inside mechanism).
4 - Back door latch bracket on lower front fixed with two screws (rare feature).
5 - Shutter release with hinged lever lock (lever missing as noted by you).
6 - Counter sunk sync contact.
7 - Extreme upper left accessory shoe placement on left hand side of camera.

I submit my finds based on above criteria in McKeown's 12th edition despite you already have found most of it:

1 - (p. 87) Japanese TLR 6x6 AUTOMAT 120 with Tri-Lausar lens and Rectus shutter, crank wind (probably Kiyabashi)
2 - (p.467) Kiyabashi Kogaku AUTOFLEX (1957) with Tri-Lausar f3.5 lens
3 - (p.923) Tokiwa Seiki Co. KWIKFLEX with Tri-Lausar Anastigmat f3.5/80mm lens in Rectus shutter
4 - (p.882) Tower Automatic Reflex are quite similar, but not identical, made by Aires, Tokyo as Aires Automat.

It should of course be noted that many cameras, especially the Japanese TLR's are quite similar, and no doubt many identical parts, including body casting, are found on a variety of brands. I imagine manufacturers selling off older tools and mfg. equipment to others for continued use, as well as original manufacturers supplying to order to several camera industries, or rebadging to order for export markets abroad.

With regards, Jan - 16 May 2009.