Peugeot J5 2.Gang scratches / Kracht very strong when switching

Dear community, I hope someone can help me, I’ve been looking for a solution for weeks; while switching from the 1st to the 2nd gear, it’s now crawling at the scraper, as if the clutch hadn’t stepped on. That came up a while ago, but then it was gone again. Now it’s all the time. It comes up as soon as you have a bit faster than step speed and want to move from the 1 to the 2nd. Not underneath. Also not with running engine and then insert the 2nd gear. with the other gears. Also a switch down into the 2nd is not possible, the crash is extreme. Only possible if it really rolls almost only, or. estimated 10km/h “drives” Some say it is the clutch, which I almost want to exclude, because the other gears work. Gear oil I have also replaced, even 2x to get out for safety. Generally it switches more easily afterwards, however, except the 2nd gear. Then they told me it is the synchronous rings of the 2.Gang. And with intermediate gas it should be gone, but it is not. Does anyone have an idea ? many greetings, maze