Using the rubber washers is of course needed to isolate the vibration. That's not the issue here. Without the metal sleeve as a stop, the bolts break through the valve cover. The sleeve limits how far the bolts can advance into the threaded inserts in the valve cover AND limits how compressed the rubber washers can be AND allows full torquing of the bolts. The sleeve is a necessary original design detail that is MISSING from nearly all replacement coils. Without the sleeve, the valve cover can be damaged, the rubber washers over compressed, and the bolts can vibrate back out. I don't know why the replacement coil manufacturers have not seen this.

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The washers help to set the depth. On factory coils, if the washers are left out the valve cover will fail as well.

I do agree, the sleeves should remain in the installation, not sure why they are omitted.

- Nick