Solved: Vignette in One corner Only
To make a long story short, my above lens (drawer) filter holder (makeshift cardboard) was obscuring the light. What threw me was it worked for 6x7 but did not work for 4x5. Removing the filter completely solves the problem.
I have not enlarged the negative again but based on looking at the projected image circle, my 135mm Componon S should cover 4x5.
Of course, now I have to mess with making 4x5 adequate holders for my 6x6 Ilford filters which should be no issue.
My hard look at the dissasembled enlarger optical parts showed quite a bit of dust on the glass surfaces, and even a fair amount of dust on the front and back sides of the lens.
I appreciate the responses.
Nice to see you got it figured out. Looks like it will be a straight-forward solution.
Originally Posted by optique