The most likely culprit is the lens. Most Wollensacks (this was a US brand with little presence in Europe, where I am based, so I am going by the specs; you might want to double check) were 4 element Tessar types, and these suffer from corner issues.
Consider a 6 element lens (Componon S, Rodagon and El Nikor have all good reputation and need not be expensive).
Just to rule out other possible causes:
check film flatness. Make a test print with a glass carrier.
check enlarger alignment. Make sure the film plane, lens board and paper easel are perfectly level.
it is unlikely you have a condensor problem (these tend to cause light falloff issues, i.e. light corners, not out of focus issues) but check that anyway. Make sure you have the appropriate condensor for your format and that the lens are properly aligned and centered.
it is unlikely your lens has diffraction issues. f11 on a f4.5 should be safe. Just to rule it out: with a glass carrier make a test print at f5.6 and f8.
A side note: I believe the corner performance (sharpness and light falloff) is overrated.
In fact I almost always burn in my edges and corners. I feel it improves my pictures, drawing attention to the main subject.