I have an XK8 year 2000 with sagging headlining. Would like to hear of a fix that does not involve removing half of the interior?  For instance, are there adhesives that can be injected behind the lining?

I had the same thing with my '98 xj. I got myself a strip of good quality Walnut looking wood 25mm wide and just a little longer than the width of the car at the back. With a chamfer on each end I sprung it in position and it actually looked pretty good. The most difficult part was find a suitable varnish to get the high gloss finish.

 

I eventually used 3M super 77 aerosol spray with a thin tube nozzle to pierce the headlining. It does the job but you can see a slight discolouration. I think this could be avoided by firstly spraying less of it behind the headlining and then letting it dry so it seals the headlining. Then try spray again and hold in place by using a small decorators roller. This second application should now hold the lining in place without showing staining. I pierced the lining in about 10 places

I used a similar spray to repair my caravan's seats that had parted company.   Thankfully the material was dark!

Peter.

I removed my headliner and replaced the fabric for £17. The spray I used wasn’t strong enough so I’ll have to do it again. When I Took the old one off, it was the foam that had perished so you’re fighting a losing battle. It is possible to take yours out and re cover it like I did. Just make sure you get a decent adhesive spray and save doing it twice like me.