Gents,
Years ago...when I had
Gents,
Years ago...when I had my shop, we would only replace the upper thick injector o-ring. The busings and corresponding seals you've removed were not part of a "normal service" in that they're primary function is to locate the injector, rather than to create an atmospheric seal. Considering the age of these cars now, likely I'd go through the trouble you're going to...and replace all the seals.
Although I have never pulled the injector holders on a Ferrari, VW and some other K/KE-jet cars used a similar type holder. On the VW, the holder which are made of plastic can be a real bear to remove...and often break. The seals are usually as hard as a rock...and can prove to be difficult to remove. Often times, the complete injector holder can be immersed in carb "cold tank" type cleaner...which will eat away at the rubber, to faciltate easier dissasembly. Note that all plastic parts will be detroyed, though.
The TR injector holders and guides can be gently cleaned using media, if necessary.
Installation of the o-rings and seals should be done with a non-silicon product...as O2 sensor damage will occur. Typically, I would use gearbox oil as a lubricant...as the injector will fit quite snugly in the new donut seal.
FYI, the donut seal is not unique to Ferrari, as it is the same as (virtually, as far as I remember) every other K/KE-jet car made.
Regards,
David