Simon don't waste your time. Once the bleed and refill stops working on an old/cheap jack pitch it. If you're a glutten for punishment though I have one in the same shape. You can have it.
I have one HF aluminum race jack. I'm getting a 2nd one and pitching that old one that won't come back to life.
As far as Craftsman goes. Sears has done an about face on their tools and guarantee. Now you have to buy their "Professional" line if you want lifetime guarantee. The "Regular" line has a 1 year warranty. I've always bought Craftsman and had excellent results but this new warranty idea is not helping their cause.