What the heck is a spark plug seal? I've changed numerous plugs, and i've never seen a spark plug seal. Maybe one on top from the plug cable or a black rubber piece inside the socket that removes it, which is not left on the plug. Plugs only have the washer that it comes with. Maybe your vehicle had or has something on the plugs that none of mine never had. You should be able to look at the other 3 and tell what it is or was that broke. I've always taken the plug cable off, blew the hole out with compressed air so dirt won't get into the cylinder, and then removed the plug and reinstalled. My 91 crx si was simple to change the plugs as compared to my 94 GMC Sonoma 4.3. Also, i've never had to remove a valve cover to access the plugs. You should be able to get out what's in there without removing the valve cover. Just have to have the right tools. Also, if you smell something burning, it's not what fell into the cylinder. You better be sure nothing gets into the cylinder or at least try your best. If it's in the motor, it's been turned to mush and goo if it's rubber, and the smell would come from out of the exhaust, which you would'nt smell. If you smell something burning, it's inside the hole outside of the cylinder, or you've got a plug wire touching a header or something.