I have been having this nagging issue ever since owning my 96.

My brakes get a bit spongey. A few quick pumps and they firm up only to eventually get spongey again. My ABS is disabled (fuse removed) and I have recently bled twice. There are no apparent leaks in the system, nothing noticeably visible, but I still would not rule that out.

I am leaning towards thinking this is a Master Cylinder issue.... Agree?