Linhof Super Rollex back light leak

I've recently acquired a Linhof Technika 70 with 2 Super Rollex 6x7 backs. I
was testing it last weekend, with FP4+ in 1 back, and Provia 100 in the
other. Last night I developed the FP4+ (only half the Provia is used in the
other back) and I noticed bad diagonal fogged lines across most frames. I
know it's the back leaking light as I forgot to take the dark slide out for
the first 3 shots and the fogging is still there.

To better describe, all shots were in landscape mode. The band starts in the
bottom left hand corner about 0.5" up, and moves in a straight line to the
right side about 1.25" up. The band is about 0.25" wide, and on some frames
wider on the right side. There is also a larger area of fogging on the right
around here the band touches the right edge. There is also fogging in
between some frames. The odd thing is that 3 frames are perfect, 7 and 8
have good images, and 9 is perfectly clear, I forgot to pull the dark slide
again.

Looking at the empty back, everything appears to fit together correctly.
When I've finished the film in the other back I'll try a B&W film in that to
see what results I get. Any ideas as to where the light is leaking? Are
these normally problematic?

Steve Bell