Neighbour called this morning - lights went out in about half the house last night. Were back on this morning, then back out. Went over early this afternoon and checked - found the lug on one bus was a bit loose, and the screw in the other one could not be turned to tighten or loosen. Closer inspection revealed some green corrosion and signs of overheating on the bus, as well as signs of heat on the wire. Shut the power off, pulled the wire from the main breaker, and it came out of the lug with little resistance. Removed the insulator block and the first two breakers so I could bend the buss bar far enough to get a vice-grips on the screw head holding the lug to the bar, got it out and headed to the "used electrical parts emporium" (Pope Electric in Kitchener) and got a replacement lug and chunk of wire for 5 bucks - cheap at twice the price, and put it all back together.
I've never seen a house with so many "edison" circuits - over half the breakers are tied trip breakers with red and black wires - even aluminum wire was pricy back in 1972, I guess.
2 hours later everything is back to normal -they should be able to get a few more years out of the panel and mabee not need to replace it before they downsize and sell the house...