JOC in IL: the transom expansion plugs seem to be available at marine supply stores, or various Amazon or eBay vendors. Here's a stainless steel eBay example, just like what I used:
1" Drain Plug Rubber Stainless Steel Twist Turn Boat Hull Livewell Drain Plugs | eBay
78F350: Interestingly, the 986 Porsche parts catalog seems to list the spark plug o-rings and tubes as being applicable to all 986 option codes and years, with no listed exception. The 987 parts catalog does list the tubeless gasket system shown in the thread you linked.
Gelbster: Based on your information, it seems people should steer clear of aftermarket o-rings and tubes. Why anyone would purposely plan to put ill-fitting parts on their nice Porsche, is beyond me...
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