[dwathencars]

Roger. This is a common problem on older Jaguars, so I've had to free up way too many stuck plugs in aluminum heads. Here is what has worked for me:
-you are correct to try to get a lube into the threads, but I've had to use a heating and cooling process to help this. I like a torch on the surrounding head followed by spraying a freezing liquid on the plug, followed by a liquid wrench or knocker loose kind of product. It's easy to start a fire doing this.... The freezing spray seems to be the key, it's avail at autozone etc.
-more drastic is to physically break up the spark plug so that only the steel outer ring remains, then carefully cut a notch that allows it to collapse. I've used grease to try to catch the saw filings, and it's impossible to avoid some thread damage.
-most drastic is to have to install a threaded insert. I've done this severel times and it works great, but it seems like it would effect the spark plug operating temperature since the heat transfer path is changed. Good luck. Dave