DC49 - does it have a thermal fuse?

[bristol_fashion]

Hi, I bought a DC49 the other week, for spares / repair. I got stuck in & stripped it down to the last nut and bolt, testing contnuity as I went. The cable is in good, unmarked condition but when I tested for continuity between the plug and the motor - no dice! I've found that the problem lies in the removable clear plastic ring & clip that contains two circular contacts. This item has two wires that connect to the motor leads, white & black. There is no continuity between the spade on the black wire and its soldered joint with the slip ring. The culprit must be the component in the black sleeve (pictured). Can anyone tell me what the component is, and is it readily replaceable? Can I buy the whole item as a spare or should I be thinking about replacing the electrical component myself?