As i said: it can't be a filter problem, because using no filtration doesn't show grade 2 as usual, but something around grade 0.5 (estimated).
Although they shouldn't in theory, i have seen dichroic filters fade after many years of heavy use. But the filters in my enlargers are ok so far, at least they were the last time i used them before moving to the new apartment...

But i got myself some Dektol and N113 today, so i will be able to tell of it's developer fault sometime this week.