Agree with others, not an emergency, but undo them when motor is warm to hot. Use a small amount of anti-seize on threads for new plugs, being careful to not get it on the plug itself. Maybe run a thread cleaner/chaser carefully in there to clean things up. Mike

I feel your pain. Cant count how many times I have gone to remove a plug and you start having to REALLY apply torque(feels like 60 ft/lbs plus) and you start thinking, "this is aluminum and this plug is certainly starting to cross thread". Sickening feeling. But I agree with the others, soak in PB, start and get hot, soak in PB again, start and get hot, then remove. It will feel terribly similar to something cross threading....but it won't. It will come out. As an aside, I know it is contra conventional wisdom but after removal and cleaning of the spark plug hole threads(rag and paint thinner and my pointer finger), I do use grey anti seize on re-installation. Dont over-torque(I use the "just tight enough" guage). You will never have the issue again.

I'm a bit embarrased to admit, but the original spark plugs in our old 740 B230 NA were were still running perfectly fine at 90,000+ miles. You replaced the plugs in that car at ??,??? miles and it only has 112K on it now, so my guess is that she hasn't put that many miles on them. But even so, I kind of like the sleeping dog approach, as long as it's still running good. There are many things that could happen down the road in the next few years (some we don't want to think about too much) that would render a plug change right now to be wasted. For instance, what if it blows a head gasket two years from now? There's a perfect opportunity to fix the spark plug problem at that time.
I vote to leave the plugs alone and concentrate on some of the other things that an 18 year old car might need. You have replaced the radiator by now, haven't you?

Matt---I can answer your query on two counts---- "but at the same time I realize that the plugs cant stay in there for another 7 years... or can they?"
I was faced with the same dilemma about a year after I purchased my 1980 245 in 2000. The original owner had a tune-up about 15k miles before selling the car to me (at about 110K). After a year of driving I decided to do a tune-up and T/B change. #'s 1,2 and 3 came out no sweat--#4 would only budge a tiny bit and like you I tried a back and forth procedure--with no luck--and like you, I didn't want to see an aluminum packed spark plug thread. The other plugs looked ok normal for 30k miles and I returned them to keep the 4th company. The car always started normally (except for wet weather--new wires took care of that) and returned 26-28mpg on road trips--20-25 around town. It was around 150k miles later (now over 275k on the car) that the mileage started to drop (last year). I've owned and serviced many aluminum cylinder headed motors and have always tried to do spark plug changes cold. My Volvo trained Danish friend suggested a hot motor attempt--and lo and behold(!!!) the #4 came right out - the set was worn but not the worst I've ever seen.
So, in short--yes you can probably leave them in another 7 years--and yes there's a good chance they'll come out using a different technique. In your case you know they were installed correctly--I was afraid mine was cross threaded to start with (thankfully, not the case). -- Dave