Here's what the advert says:
Product Description
"ZDDPlus is an oil supplement that contains very high concentrations of the well-known additive ZDDP (Zinc Dialkyl Dithiophosphate), which has been the primary EP (extreme pressure) ingredient in all quality motor oils for over 70 years. However, beginning in the late 1980s, the concentration has been greatly reduced as newer oil classifications have come on the market. ZDDPlus is the ONLY EP (Extreme Pressure) component which re-establishes the ZDDP levels that classic car engines were designed for, while allowing the car owner to use the base oil of their choice. ZDDPlus also alters bearing and journal surface characteristics to prevent metal to metal contact. Under extreme conditions like a high performance motor, ZDDP reduces the tendency of parts to scuff or gall under heavy loads. While some off-the-shelf additives may have some ZDDP but the amount per bottle is small. ZDDPlus is not a typical oil additive. It is compatible with all conventional and synthetic oils intended for automotive use. By adding a small 4 ounce bottle of it at every oil change, an adequate amount of Zinc and Phosphorus will continue to protect your engine."
Over at the GL1800 forum there was a lot of discussion about Zinc and cats etc. The GW can be crunchy when shifting gears. I've used it in my GW for a couple of years and no ill effects yet.
Can read some of the discussion here:
ZDDP observation - Page 2 - GL1800Riders
"Ghost shifting" btw is popping out of gear. I never had this happened on either bike...
cat