The problem is solved, turned out the pre owner took a normal transmission of MC21 but with HRC shifting forks, the forks, especially L and C are different, R could be same, I actually did not measure.
After I've found out the issue I thought about buying complete transmission or only shifting forks, at that time in Japan there was a complete MC28 wet transmission I've bought at an auction. Three of the gears have a different ratio (doesn't bother me), counted the teeth of the gears when it arrived last week.
As i did not disassemble the MC21 transmission with the shafts and gears, I wanted to make sure there are no other problems than the shifting forks and so I reasselbled the engine with the complete MC28 transmission I got from Japan. It was very "mechanic friendly" to reassemble. The other thing I corrected was the missing clutch basket nut washer (OUTSIDE washer).
Now I took also 10W40 as transmission oil, had no 10W30.
End of story, the NSR now is completely assembled and shifting without any problems. Very happy now.
Will search for another set of shifting forks for the standard MC21 transmission which I want to put back as a spare part.
Thank you for your input and kind Regards, will post pictures soon.