Don't spend your money on a cartridge BB yet.
I would be willing to bet that that bottom bracket shell has damaged threads.
As you are replacing bottom brackets anyway, the best solution is to
- Get everything apart, including the fixed cup (backwards thread!). That one might come out easily, but if not and you don't have the tool either go to a bike shop or take a high tensile bolt with corresponding nut and tighten inside the fixed cup. With enough swearing and tightening from both sides, the fixed cup will come out.
- Clean everything and confirm the thread on the BB shell is damaged.
- Don't mess around if the thread is damaged. At best you will be retightening it all the time. You need to go to a framebuilder, and get the shell faced to accept one of these :
