not sure where to put this so I'm putting in here, but i had to change my pinion seal and cover gasket. and I'm ready to fill it up but...the fill screw is rounded out so I'm not sure what i could do to get the screw out of the back so i can fill it up. thanks

 

is it an allen bolt? or a square? hex????

what year is the car?
10 bolt? 12 bolt? pig type? or inspection cover type?

Hard to say with so little info!!!!

 

its a 85 monte carlo ss, 3.73 posi, should be a square but cant tell cuz whoever owned it before me rounded it i guess, 10 bolt and im not sure what pigtype/inspection type is. here is the cover though if that is what your talking about,

Buy Dorman - OE Solutions Rear Differential Cover 697-701 at Advance Auto Parts

 

Ok thats a 10 bolt inspection cover type:
Meaning you have to tear it apart by removeing the pins spider gears C-clips axles etc....

I have 2 solutions.....

solution 1)...If theres enuff of the plug left...try vise grips? to get it out..and then replace it with a new one...once u get it out...

solution 2).... Purchase a new inspection cover that has the plug built into it...

 

Drill out the center of the plug, and use an easy-out (bolt extractor), penetrating oil and heat (if needed).

 

I dont think thats the best idea....

Wheres all the chips going to go especially if he drills it all the way thru..(Depending on how much is actually left of the plug!)? also that plug is made out of cast steel...(pot metal).....I dont believe its composition is as such to hold that kind of pressure....of an easy out...Since its already messed up...

My best and safest guess is that it may even be either cross threaded...or overtightened at 1 point...which is the very reason its currently in the shape its in?

Other wise he will have to disassemble..the whole thing and start all over cleaning out all of the chips ,grindings peices etc....IMO

 

X2 , You should heat the plug up with a troch then try to remove plug.
Use a hammer an punch /chisel to turn plug like your removing it.. . , You may have to drill
an use easy-out . I have done this many times on Mail trucks ..