Those rubber rings are a spacer/insulator. They hold the nose of the
injector in position and reduce heat transfer from the head to the
injector. If you didn't have them in there, you would have had a vacuum
leak. But fuel doesn't leak out of there.
Probably the injectors came loose from the fuel rail, as it would have
only been the o-rings holding them in, and fuel leaked from the top.
When I first fired up my engine after it had been sitting for a few years,
the o-rings had shrunk from being dry for so long... leaked like a sieve
Cheers... jondee86
1984 AE86 Corolla GT Liftback, NZ new... now with GZE
spec small port, twinscrew s/c and water/methanol injection

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