Nathan, check my comments about the felt seals below the pressure plate.
No seals on this one. Interestingly, instead of circular holes, the pressure plate has U-shaped cutouts that go all the way to the edge---an economy measure, I suppose; if I keep having problems, maybe I should attach a strip of felt or velvet along that edge.
San Diego, CA, USA
The lady of the house has to be a pretty swell sort of person to put up with the annoyance of a photographer.
-The Little Technical Library, _Developing, Printing, And Enlarging_