Hard drive and TechTool PRO

[FrancineMack]

I sometimes boot using OS 9.2.2 so that I can use TechTool Pro 3.0.9. When I
do that I get a message about scanning blocks on my drive. When I run that I
usually get a message that the repair was successful. I am concerned that
this has been necessary quite often (more than five times). I have also
received a message that the problem could not be fixed.
When I boot in OS 10.2.5, I often use disk utility to repair permissions.
Could this mean that my hard drive is about to become toast ?  If so, I need
to try to buy a new one that is not too expensive. Is a hard drive
considered to be something that an owner can replace?
TIA,
Francine