It could be the light source itself. If there isn't enough blue in the source, no amount of filtering is going to give the necessary contrast.

Any chance that there is a yellow filter stuck somewhere in the light path?

What condition are the diffuses in the enlargers?

Did you buy the enlargers used, from a devotee of the work of Mortenson ?

EDIT: Oops - just noted that they had been used by you successfully before. Did you somehow become a a devotee of the work of Mortenson as a result of your recent move ?