First thing to realise is that lubing without cleaning the old stuff off will just make matters worse, as all you're doing is making extra grinding paste!
After you've cleaned the rubbers and mechanism as best you can (WD40 as a solvent and a cloth/brush), then lube the rubber with silicone lube, available from B&Q, in the drainage section - it;s designed for underground pipes and is great stuff, a little goes a long way.
Then, use something like Silkopen, which is a graphite-loaded penetrating spray, for the mechnism. It evaporates to leave a layer of graphite behind, giving long term lubrication.
Cheers,
MIke