Just what is a Model A Black & Decker Drill ?      Unless its one of them large gear reduction 1/2 drive drills it isn't worth repairing.  The new drill motors are a lot smaller, lighter, reversible, and more power.   You can buy a top quality corded drill motor 1/2 in. drive for around 200 dollars.  I have a newer HD corded Milwaukee in my tool box and it just never gets used because all I ever use anymore is my cordless drill motor which is 1/2 drive.  One of the big things about having good luck with drilling holes is sharp drill bits.