Rear brake bleeding tab broke off, now leaking fluid

[whytry]

I was bleeding my rear brakes at the house with the 1 man vacuum pump and for some reason it would always have air in the line even when the bleeder was supposed to be closed and screw'd in. I thought it was the bleeder, so went and bought new ones and still did it. Tried another bleeder and this time the tab on the drum brake 'backing plate' (not sure of official name) where you screw the bleeder in broke off, it looks like it had a crack in it already and this was where it was leaking from... Now it's broken off and slowly draining the M/C out. Is there a way to stop it from leaking all the new fluid out? Right now I have a towel wrapped around it and then I taped the towel as tight as I could with the bleeder pushed in place, let go it falls out and leaks faster, hence taping it in place.. So it that something that can be fixed? Or do I need to new backing plates or whatever the part is called where the bleeder screw is... Also if I need a new part, can I just go to the local parts store (I doubt this but thought I would throw it out there)..