Michael, if I understand what you are saying..you see a change in prints from previous print sessions, correct? Would question first, since you say the developer LPD, is the same, is it from a new batch since you noticed it? 2nd, is the paper from newer lot numbers, since the re-org of Ilford? Of course the fixer should be checked as well as the toner, but it really sounds to me you have checked most of the obvious possibilities. Why not contact Ilford and see what they have to say, sure they would be interested in hearing about this.
Do let us know if you find the cause or if there might be a slight change in formulation.