Thanks for the information. I tried getting close to 5.2 ms specified value but the curtain wouldn't have enough tension to complete it cycle, and ended settling on 3 ms (the original was around that).
I have finished assembling the camera now and it's working fine although speeds lower than 1/8 started sticking up again. The light seals have been replaced with yarn and felt. The lens is a 50 mm f/2 Yashica that has some fungus and some damage from what it seems that someone tried to unbend the barrel. I would normally try to clean it but this lens model normally has the barrel nose screwed so tight that in my experience it requires some destructive methods to remove it. The leatherette has been replaced from a couple of scrap cameras.