Failures were quite common with the original design mounts, which were made from good old fashioned rubber. They were more compliant (softer) than the later urethane version, but like most rubber they would break down over time and exposure to things like ozone, used motor oil dumped on them when changing the wonderfully placed oil filter, etc. I can't remember exactly when Harley updated the material, but I though it was around 2006. Personally, I changed my 2005 out and used an aftermarket urethane product. It is less compliant and transfers a little more vibration to the frame, but it's pretty much resistant to chemical attack.
I'm going to beat a dead horse again, so this is fair warning to those who don't appreciate my comments. Like many of the other parts on my and other Harley's that require replacement way too often, I find I don't have that same issue with the automotive products I've owned going back to the 60's. Never once have I had to change a motor mount on any of my four wheeled vehicles. And the oldest ones used materials not much different than what Harley used.
Jerry