i have bought this lens, and it is in ok condition. rear lens is very nice, front group needs cleaning.
its a heliar design .
do i approach it by unscrewing the ring in the front (pic 1)
or by unscrewing the whole front part (seems like somebody has tried this before)
seller said that it would profit from a thorough cleaning in the front group but that he wasnt able to open it.

any advice?
thank you,