Your bike uses a HyVo chain. It should not wear out in 20,000 miles, they should last the lifetime of the engine. If it is worn out it would be the fault of a junk cam chain tensioner. I do know about those since I've been involved in making tensioners for Kawasakis and now Hondas for the past three years. Automatic tensioners mostly suck in design, especially the ratchet style. That is how I got into this, junk tensioners in two of my bikes.
Measure your cam chain over the prescribed number of links to see if it actually IS worn out or if you are dealing with a JUNK tensioner. My bet is at the least the tensioner is junk, possibly chain too, but possibly not if you're lucky. There is no way in hell I'd ever put an automatic cam chain tensioner back in a bike if the cam drive failed. I went through two OEM tensioners in my KLX650 in less than 14,000 miles, the last one allowing the cam chains (2 on the 650) to wear beyond tolerance.
After installing the manual tensioner I have over 30,000 miles with only about .050" adjustment made as the new HyVo chains seated in. Virtually no adjustment in the past 10,000 or more miles... I forget when I last did it. You adjust the tensioner when the engine is at full operating temperature if the cam drive ticks, not clatter, but ticks. I also had to put a manual tensioner in my Zephyr 550 - that was actually one I had to make so when I did I made five of them and sold the five. It kind of blossomed.
If you want to take care of the tensioner issue, contact me and I will see what can be done for a manual unit for less than any other company will sell one, probably $30 plus shipping. I have fitted one for a YZF425, but don't know if it fits up to any others. It is identical to that of a KLX650, but uses a different thru bolt set up which is no big deal. All I need is the pattern of the tensioner body.
Here is a sample of my work in a KLX250:
If you want references for my abilities should you need them, just do a google search on Krieger Cam Chain Tensioners. Like I said earlier, it kind of blossomed. I've sold tensioners in 29 countries and I think now to all 50 states in the U.S. and all provinces of Canada, to the tune of around 700-800 units. You'll find a lot of satisfied riders, including some on this forum. You may find where I worked with a KLX250/300 rider to make the tensioner (apparently the only one available for them). I can help if needed. Email me from here if you wish.