Try this on the 40-year-old tub drain (should be threaded):
1. Take a hacksaw blade and cut a small 1/4" V notch in the inside edge of the drain.
2. Heat the drain with a hair dryer on high heat to soften the old plumber's putty under the drain lip.
3. Put the end of a flathead screwdriver or small chisel in the V notch and tap the drain around counter-clockwise with a hammer to loosen it and turn it out.
4. Clean off all of the old putty in the depression around the drain hole.
5. Roll a roll of fresh plumber's putty in your hands about the size of a pencil and wrap it all around in the drain hole depression.
6. Tighten the new drain down on the putty, being careful not to break the crosspieces. You can use a tool made for the purpose, or you can carefully use the handles of a pair of channel-locks with a screwdriver in the teeth for leverage to tighten the new drain in. Wipe away and save the excess putty.