Scott, although you may not find any direct statements of insurance/guarantee relating to the faulty plenum causing damage, and they just mention guarantees of failure of the plenum iteslf, the product would still be covered under the sale of goods act.
If the product is not fit for purpose and fails then the seller would be liable not only for the cost of the product, but if damage to any other component is directly attributable to the faulty product, they would also be liable for repairs to the other components. This is why the R&D is a highly important process. Although it may seem like some have put a dampener on this product, I feel they could be sving you from a VERY expensive legal minefield.
Though if you do press ahead with the product, I can only suggest that you consult with an appropriate legal representative who should be able to inform you of all the necessary insurances you will need.
It may also be the case that as the part is integral to the safe function of a motor vehicle that there are certain standards and tests which have to be passed in order to legally sell the product. This is certainly the case with tyre manufacturers, brake pad manufacturers and wheel manufacturers etc.. So could be worth some more investigation before placing this on any road going vehicle.
The above is meant to be constructive, so please dont construe this a poo pooing your idea.
+1
Possibly a way out of this though is to merely be a distributor of the plenums as you do not manufacture them, this way the carbon company would take the responsibility. im not saying you should go without the relevant protection, just a thought.