The bit about remedies like this that I don't understand is: You swallow the oil, it goes into your stomach where it's acted on by very efficient gastric acids, then it somehow knows that it needs to survive that unscathed and go directly to your (knee) joints and act as a lubricant? Something about that doesn't quite ring true to me, and sounds like sympathetic magic (which has been shown to work almost universally in all sorts of ways, it's true) so maybe I'm just being naive here.
Cod liver oil's cheap, but glucosamine and the like isn't, and that's the bit that worries me. Why not take a teaspoonful of sunflower oil every day, even cheaper and just as effective as a placebo perhaps? Before condemning that idea, just test it?