So i replaced the plastic housing with a new aluminum one. This one seems better than the one i used 3 years ago on the first xk8. However, they included an o-ring for the cap seal and that should be a flat rubber washer, but I used the o-ring but am leery of it.

For anyone doing this you should buy the two o-rings C2C11477 for the outlet pipe and a new bypass hose NCA2213AC. The OD of the plastic tube is 42 mm and the new aluminum is only 37 mm. So the old bypass hose will likely leak as mine did, as it was stretched to fit 42 mm.