I had the same problem a few months ago and asked about it here, search for "Holy Bellows, Batman!". After getting some good advice, this was my solution and results:
I went to the Dive shop and bought a tube of Black Neoprene cement for fixing wetsuits. Luckily, the woman behind the counter had studied Photography in college (and is an analog advocate) and understood the problem.
The bellows was in worse shape than I first thought with the vinyl(?) coating cracked at all the corners and corner seams. I have put three coats of the cement along the seams and then dusted it with talc so that it wouldn't stick to itself when compressed. It seems to have worked very well. The results are like Night and Day . It flexes well and doesn't inhibit the movement of the bellows. I'll watch it for further problems but it looks as if I've bought myself some time for a mere $5.50. Just to be safe, I will also hang my darkcloth over the bellows before pulling the slide. Hey, you have to put it somewhere while shooting, it might as well be doing some good.