Hektor 13.5cm disassembly?

I'm stumped on disassembling the optical group/aperture of my Hektor 13.5cm lens. It has a stiff aperture ring that needs to be cleaned. I can remove the front optical group but nothing else seems to budge. There is one set screw around the aperture scale, 2 set screws around the aperture ring and that's it. I'm sure the rear group can be unscrewed but it's really tight and I'm waiting on the right size rubber grippy to loosen it. There are many lenses with guides but this doesn't seem to be one of them. Help?

Thanks!

Update on this-

I finally got it apart. The aperture scale was nearly glued to the barrel with old grease(?) but with a little mechanical persuasion, it came loose. The aperture selector ring was next. Two through-hole set screws and the ring will unscrew. This one was very tough to unscrew. After getting things back together, I believe it has an out of round barrel. The aperture retaining ring on the inside can be pulled straight up. The barrel also unscrews but this isn't necessary. Clean the old grease off of the aperture retaining ring and inside of the barrel, relube lightly and replace the retaining ring. Be sure to line up the set screw holes with wide open on the barrel slots. Clean the aperture selector threads and grease lightly. Screw back down and line up with holes, replace set screws but don't screw them all the way down as they will contact the lens group and you will not be able to move the aperture selector ring. Replace aperture scale with set screw and screw in the front optical group. Done!