Originally Posted by Zillon
I wouldn't sweat it too much, honestly.
In the US, (thanks to the Magnuson Moss Warranty Act) to deny a warranty claim due to aftermarket parts, they would first have to prove that a specific aftermarket component caused the failure in the first place.
If anything, a stiffer rear mount should prolong the life of the other two motor mounts. I'm not sure if there's an equivalent of the MM act up there, but I'd look into it if you're really that worried.
I've heard of that one before, and it just makes sense. It's not really that I'm 'worried', rather I'm playing it safe. I bought a new car for warranties, and it is basically the first year of the model so who knows what could be encountered down the road as these cars get mileage on them. The mount is definitely an attractive option, in terms of price and reported improvement. I will be looking into it for sure.
If anything I should be more worried about my parents who would definitely get worried as to what I'm doing to the car.