In my most humble opinion and theory. This is what happened (is happening) with the harness. In the late 80s there was a large push by environmental concerns primarily in Germany to make more parts of the automobile recyclable, including the harness. You all must have seen the lettering on the plastic parts which identify the type of material (PA-GF) etc. What has most likely happened is the compounds used in the insulation were changed to allow the plastics to be removed from the copper wiring chemically in some sort of vat. I am sure there was lots of testing prior to the release of the new wire but something was missed obviously. I have no proof of this, it is just a theory but it all adds up.

Problems in the vehicle due to the harness defect vary greatly. Misfire, damage to control units and actuators etc. If you even suspect a bad harness replace it, the HFM, TT/LLR, EGAS units are expensive. BTW, the short harness to the throttle actuators also often exhibit the insulation failures.

As far as the automaker.....there is no way in hell that anything will be published by them officially, putting them on the hook for millions of dollars in repairs and bad press. Push them to sell you the harness at the absolute bottom line price, even at cost if you can. Install it yourself. On a 104 motor it takes less than an hour.