Interesting, John. How many years do you figure they were good for? My only experience with poly bushings is the IPD poly bushing blocks that come with their front sway bars. They give you a poly compatible grease to use. After a number of years it dries out and you'll start getting front end squeaks over speed bumps. I imagine that's a hint that wear is likely taking place. That's long been on my do list to re-grease and your post now reminds me to put it to the top. You can't just use any old grease, it's supposed to be a silicone based grease (typically PTFE additives), not a lithium based grease (typically with moly additives). As much as there's not a lot of movement in the accessory mounting bushings, for those who do use poly bushings it might extend their life to initially apply lubricant as a surface protectant. After your post I'm definitely going to keep staying with the rubber bushings as I always have. I'm uncertain if there are significant differences in the aftermarket rubber compounds. At least for the alternator they're quite easy to replace so the difference between a 6 and 9 year lifespan isn't a big deal.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now