Thanks a lot for all hints!
I have called my friendly local photo doctor. He gave me some diagnostic steps to identify the problem. Most of it are already mentioned in above responses.
1. Filter in out lever to check change in the light colour.
Result: Working as supposed to be.
2. Clean movement of filter in light path: Result: colour seems to be changing gradually but there i no way to check if it is changing at the rate is should be.
3. check bulb:
Result: found a decoration type halogen lamp instead of photo bulb. I guess previous owner wanted to save some money. Changed it to osram 100watt photo bulb.
Got a box of fresh ilford VC paper. Did step wedge prints of all grades. Now i see grade from 4.5 to 0 (RN: 70 to 145). GREAT!
opened fresh Forte polygrade V fb paper order from BHphoto in December 05. Result.... I still see grade from barely 2 to 00 (RN: 175 to 115). Surprisingly with no filter in light path i get grade 1 but with magenta-40 i get grade 0.5.
I can leave with grade 2 contrast but i need to understand why this is happening. Is the paper not good? or worse is it fogged slightly?