I finally managed to service my copy of the 20mm f/4 - and I had a much tougher time than Ric. Experiences shared
https://whatdoineed2do.blogspot.com/2026/01/widely-regarded-nikkor-20mm-f4-ai.html#servicingServicing this is an utter pain - i've had 2 copies of the K (103xxx and 106xxx serial numbers, with Roland data saying the first one was 1030001) and they're both sealed so well its like they didnt think these lens would need to be ever opened again.
The focus ring retaining ring does come off and I had to file slots behind the ring to get to the focus ring screws and the lens objective needs the strength and torque of all humanity to unseat. BUT its done - i finally got in and was able to save these 2x lens from a life in a junk bin.
TLDR: its hurts, dont do it unless you have the tools and know exactly what you're doing - you'll damage a beautiful little lens and its not worth it