I first tried a Holga back in '99. I too did not think light leaks were part of the charm and proceeded to tape/fix the camera. As others have said, it was $20.
As to 6x12 if one already has the means to shoot 6x12, there's not much point i.m.o. If one doesn't have a roll back that can enable 6x12 there's not a more budget friendly option.
My holgapan 120 is also modified to take a 90mm view camera lens. Mine does not have any light leaks (it was fine pre-modification as well).
As much as I recall, the "weak points" in almost all Holgas have been the back retention/strap lugs and the red window. 1 piece of tape, and a rubber band fixes both "issues."
If one is simply after pinhole photography, I think there are too many options to discuss but laser drilled aperture sets can still be found which lets one turn any lens cap or body cap into a pinhole lens.