Most Sportsters that I know of have these replaced at low miles. The cheap paper gasket's HD uses leave a lot to be desired. Mine were done at 1500 miles. It was still under warranty at the time, so had the dealer replace them.
I had to replace both sets of mine between 3600, and 5900 miles. The rear one went first, and about a thousand miles or so later I had to tear into the front end.
Do this job yourself, and save some severe bucks. It took about 2 hours to do the rear cylinder, and about 1 hour to do the front.
Buy you a friggin' service manual, and handle it yourself.
If you are too much a GEEK to handle this little lesson in mechanics, then you should be drivin' a friggin' Geo.
When mine went out , it was still under warranty, therefore had the dealer do them. I do have the service and parts manual to do my own repairs, and now that the warranty is up will do the work myself in the future. Have been a gearhead all my life and not afraid to tackle most jobs.
As for the geek and Geo comment, never considered either in my life and to old to change my ways.