Yet another Zeiss Jena Tessar 50/2.8 disassembly inquiry

[JJB]

Hello all, I have scoured the internet and done a search on this forum and am unclear about how to proceed as most Tessar 50/2.8 lenses depicted are of a different vintage and/or mount type. I have a CZ Jena Tessar 50/2.8 aluminum lens with Exakta mount, circa 1950s. As one might expect, the focusing ring is very stiff. I would like to disassemble the lens only as far as is necessary to access the helicoid to clean off the crud and relubricate. The aperture ring turns freely and the blades move as they should.

The problem is that this lens has no obvious screws other than the two small screws that help to secure the lens to an Exakta mount camera, one on the rear face of the lens and one on the side of the barrel. These I have removed. As far as I can tell, I have two choices, I can use a spanner to try to unscrew the central element from the rear. Or I can go through the front by removing the rubber-like name plate and see what's underneath. I have seen Rick Oleson's extremely helpful diagram that illustrates all of the lens's parts. What I would like to do is to get to the starting point in this thread and to not take it apart more than is necessary:

http://forum.mflenses.com/tessar-50mm-alu-reassembly-t11938.html

Then I can carefully follow the instructions to put it back together again.

This lens was inexpensive so I'm not afraid to experiment. I have a second identical model which is pristine in its original box, also with very stiff focusing, and I'd prefer to make my mistakes on the cheap one. Thus far, I've only taken apart and reassembled two lenses - an Industar 61 and a Mamiya Sekor 50/2. I have most of the basic tools recommended in this forum's very helpful sticky on the subject.

Here are some photos of the lens. Many thanks in advance.