Leaking light seals are a hazard with the SQ series backs. The originals were a foam that slowly reverts to goop.
If they are badly deteriorated, it may be hard to tell what was there. Jon Goodman, doing business
on eBay as "Interslice" has an excellent kit of light seal material. Items #1 & #2 here are strips of approximately
2 x 2 mm foam about 2 cm long, installed in the grooves. Item #3 is an adhesive back cloth material approx
6 mm wide and 7 cm long, it is less likely to be bad, but replacement material is in Jon's kit.