Your seal on your master cylinder can also be starting to go out on you slowly , just enough so that its starting to get that spongy feeling to it.I think there is a bearing in the part just before it joins into your brake booster , and that is the part ot look into.

1996 Jeep Grand Cherokee 5.2 with mods.Hughes Air gap intake , 52MM TB , ford injectors, 2 3/4" lift, Doug Thorley headers , HID headlights with LED , HID fog lights , glow gauges , a few others