A friend of mine has a Honda Odyssey with “100,000 mile” spark plugs. As anyone can guess, the van has 120,000 miles on it and the plugs have never been touched. How might one remove them without risk of damage. I thought of spritzing a little PB Baster penetrating lube into the wells and letting it sit for a while. Think that would work?
I take my plugs out every 30,000 miles or so just so they don’t seize, but my friend never did that, and I fear that if he tries to get them loose something might break off and end up in the cylinder.
The only way to find out what will happen is to try to remove them. Penetrating oil applied a day or two in advance will help with potential success in removing the spark plugs. Also, you do not want to try to loosen them when then engine is hot unless you are a member of the extra-work-is-fun club. That is a surefire way to bring the threads out of the head with the spark plugs. If you do that, then you will have to replace the entire engine 
If the van has been driven the day you are to work on it, wait a couple hours before you start work. If you can comfortably rest your fingertips on the bare metal of the cylinder head, and it feels warm, not hot, to the touch, it is safe to work on. You may have better luck if the engine is this warm rather than stone cold, but either is okay. Hot engine is not okay.
100,000 mile spark plug changes = another bad idea from auto engineers. Yeah, you save the cost of one spark plug change (vs. a 50k interval) but risk ruining your cylinder heads when you try to pull the original plugs at 100K+ miles.
I recently changed my Odyssey spark plugs after 100,000 miles and they were still in great shape. I had taken them out previously and put on anti-seize compound on the threads, but I doubt your friend will have much trouble.
Maybe because of the way the coil/spark plug boot fits over the spark plug, moisture and corrossion shouldn’t be as much of an issue compared to older engines.
100,000 mile spark plugs are the norm for cars these days, and there is no more risk of cylinder head damage now than there was at 30,000 miles. Aside from certain Ford V-8 engines, spark plug seizing and head damage is a statistical improbability that you shouldn’t even consider.
Many Fords come equipped with 100K mile platinum plugs. Changing them is seldom a problem…Today, most spark-plugs use a tapered seat which forms a perfect seal. No amount of PB Blaster can penetrate a perfect seal. That’s a waste of time. The penetrating oil will never get to the threads. After you break them loose, THEN a little Blaster can do it’s job and make removal a little easier and reduce the chances of thread damage. Instead of using 3/8 inch drive tools, try using 1/2 inch drive sockets which provides the leverage needed to break stubborn plugs loose. An often overlooked technique is to TIGHTEN the plugs a tiny bit first THEN back them out a quarter turn THEN spray some Blaster on them…
Consumers are fed up with high-maintenance automobiles. In the near future, cars will gravitate towards the goal of ZERO maintenance (like your dishwasher and washing machine) in order to sell their product in a VERY competitive market…
I like things that are ZERO maintenance as long as they last as long or longer than things that require maintenance. My parents bought a new Sears Coldspot refrigerator in 1939. Every 2 months, my dad would oil the motor. Even so, the motor burned out 10 years later and we took the motor to a shop to be rewound. My present refrigerator is 16 years old–the unit is sealed and it has required ZERO maintenance. In spite of my love for old automobiles, today’s cars require a lot less maintenance and do last much longer.
I’ve never seen a 100k miles spark plug yet that was actually good, even in spite of the engine running apparently fine with no misfire codes.
Just like shocks and struts becoming weak with mileage engine performance also degrades a bit. Sometimes more than a bit.
The odds of something falling into the cylinder is near zero but the odds of plugs seizing in the threads are much higher.
Sometimes removal of the plugs will damage the threads no matter how careful you are. In a case like this the threads can be repaired with a thread insert although judging by posts on this forum over the last few years some misguided souls seem to think that replacing a cylinder head or an entire engine is required.