Need advice: Stripped glow plug threads
I was supposed to do a quick glow plug service on my 159 1.9 8v, but that plan soon came to an end when some of the threads on the second glow plug came out with the plug itself. (2nd plug counting from the cam belt). I replaced the plug with bad threads with a new one, but as I started to tighten it the threads snapped. The plug is still mounted, and the car runs just fine, but I have to get this sorted.
After talking to the best Alfa garage in the area I have some alternatives, but I need help to figure out what to do.
Alt 1. Take the head off, drill out threads and replace with Helicoil. A very expensive job. About £1000
Alt 2. Buy a used head and replace. Still very expensive, but maybe a bit cheaper than alt. 1.
Alt 3. Use a slightly larger tap to enlarge the glow plug hole, and replace the glow plug with a larger one. What plug should I use then?
Alt 4. Use a tap to refresh the threads and get hold of some strong Loctite that will keep the plug glued in place. This will maybe be the easiest and cheapest fix, but will it hold?
How do I deal with this? What would you do?