Loosin brake fluid in rear driverside tire looks like in drum brake peddal to floor cant stop

Sounds like the brake wheel cylinder is leaking check the master cylinder and it will low or empty.

sounds like the wheel cylinder busted.

its obvously draging air in from somewere so to start with replace the bleeder valve under the hood, top up fluid bleed again.have somebody slowly pump the brakes then check all pipes and joints,hoses for sighns of leaks, if you find a leak that is the most likely spot were air is entering the system.

Master cylinder is the only thing that could cause a catastrophic brake failure.

the master cyclinder is divided into diagonal wheels. meaning that each line from the master cyclinder provides fluid to a front wheel and rear wheel. on the front resevoir of the master cyclinder it would be perhaps the left front and right rear brake for example. you need to block the lines going to the rear wheels independently and then bleed the brakes again starting with the wheel furthest from the master cyclinder.

You need to bleed the brakes. Starting at the furthest brake from the master cylinder bleed the brakes, ending at the brake closest to the master cylinder.

that sounds just like a leaky none return velve in the master cylinder or very low on brake fluid it may even have got air in the system also if you removed the rear drums and never ajusted up the brake shoes this could give you this problem check the rear brums first the brake shoes should just be tuching the drums if there not pull off the drums and wind up the ajusters then refit the drum till the drake shoes are only just clearing the drum i know they have self ajusting shoes but half the time they just dont work very well so ajust it by hand,, the front brake are disk's and they are self ajusting,,,
after doing this work leave the car for a minue or so and stamp on the brake to pump them out if you then need to pump the brakes up again that shoes its just ajusted the rear drums,,,the brake pedel should only ever need to be prest once never pumped up,, if this dont help you out and sort out the problem then and only then replace the master cylinder as there normaly very strong and dont brake down often and they often leak brake fluid first,,,my bet is its the rear shoes needing ajusting up

find the leak first and then make a reply posting and i will tell you what to do,remember that iam on gmt+1 time zone for a reply

make sure the rear shoes are manually adjusted up properly ,then is still no good renew the master cylinder because the seal between the front and rear chambers could have gone ,but i do feel that you should manually adjust the rear brakes up properly,slacken handbrake cable before you do this though

have your lines checked for leaks. if the rear brakes are drum brakes check your wheel cylinders (look under the back of the car and if the back of one tire is dry and ther other is wet and its all up into your wheel well theres your culpret). check your brake calipers to make sure fluid isn't slowly leaking past the piston (that could get ugly VERY quick and you would lose brakes and it always seems to happen on a hill too) if those are fine i would check your master cylinder