So, I found the manual from AKG with instructions on how to dismantle the K301:
http://www.akg.com/mediendatenbank2/psfile/datei/20/k100_200_34055d23d12c1d.pdf
The infamous AKG elastics were dying of old age so I took some photos changing them.
First step is to open the cups. Use a screw driver or similar tool and press the latch from the inside, at the same time pulling the cap downwards:

Should come off with some push and pull.

Then it's only to cut the rivet end and old elastic off and tie some new elastic around the rivet. Old elastic:

New elastic:

Ready for use.ericj's suggestion of covering the baffle's outer ring of holes - see pic below - with felt is well worth trying.

The fabric pads of K501 (or K601/K701) will also make a drastic change of sound, smoother, less honky and more detailed but with less bass.It won't turn the ugly duckling into a swan, but with the felt and further cup damping a much better headphone.
