Spark Plug Seals

The Bosch ones that are on my car have remained pliable for over ten years.

Some are made of silicone rubber and last a long time like Danny's.  For many years I used the boots for a Plymouth Valiant 6 cyl engine. They have a big flat and flexible disc which covers and conforms the those tin contours you mentioned.......Bruce

I wound up buying some seals from aircooled.net because their picture on their website looked better than others.

The old ones were distorted and loose on the wires.  The cooling air blew them away from the openings.  

I put zip ties around the new ones to try to squeeze them tighter on the wires.  I think I will also put zip ties on the wires right behind the seals to keep them from sliding.

I used my borescope to look at #1 & #3 to check if they were sealing.