wideguy

Cam chain guides typically last a very long time, 20 years or more without problems. This is because they are simple devices. The tensioners, that apply actual pressure to the guides to eliminate slack in the chains, are also simple devices and don't often fail.
If you're going to check your valve clearances, you can, while you have the valve covers off, check to see if your cam chains are tight, or have slack. If they are tight, it means the cam chain tensioners are working.
I've found re-installing the SV cam chain tensioners to be a fairly difficult operation. As always, easier the second time around. You can easily make the cam chain adjuster locking tool for re-installation.