Hello, Matthias.
Are you getting a full range of tones with you results, albeit at Grade 2, e.g. are shadows muddy at all. If your tones look good it would seem the developer may be ok. I breifly had an LPL enlarger with the multigrade head which appeared fine, but I also could not get beyond @ grade 2 at the maximum setting.
Also, are your bulbs ok, a spent halogen bulb won't bring any joy.
Regards, Mark Walker.