Not a race car but Ive hit a wall and need some help. 96 Chevy 1/2 ton 305. Right rear brake line keeps getting air. Wheel cylinder is NOT leaking. I can bleed all the brakes and 10 minutes later or next day the pedal will be soft and ABS light is on. ABS will also cycle periodically with very little pressure on the pedal. I cant find any leaks and fluid level doesnt drop so I cannot figure out where this air is coming from. Since this problem started I have replace wheel cylinders and master cylinder and have bled the system probably a 100 times. Any input would be greatly appreciated.