Just purchased a used 2003 Magna Executive series 2 a couple of months ago. The roof lining has just started to fall away at the rear about 15cm square. Is there any way of fixing this before it gets any worse.

Do a search of this forum and you'll find more help TD.

Is there any way of fixing this before it gets any worse.

No.
Your first mod of your 10 year Magna can be to remove the headliner and retrim it.
As above, plenty of "how to" help if you search.

I paid $180 to have it done professionally. Good price in the Newcastle area to the other 3 quotes I got. Hope that helps.

If you're on the Gold Coast, AAA trimming do roof linings. Ask for Alex and say Dan sent you.