Foco zx250 rotator

Hello, I have such an old focon loader that I put in a forest cart. now it started leaking under the boom turner under the big "hit nut", a couple of times when I tightened it it stopped leaking but opened by itself after a while. Finally, oil leaked even though I tightened it, what kind of gaskets are there and has anyone else repaired the item in question. There is a gap in the vertical post also at the top end, could that have an effect on the turning motor leaking? Sorry for the bad English, I use google translate.

[Jac]

There are some threads here on the forum but it seems like the main seal is not possible to find anymore
Peter Persson @ Bamse, nytt projekt!
lennartostman @ Foco kran läckande svängmotor