Q: ipod video 30gb has hdd problems

Since you mentioned the size coming up as something odd, there's a small possibility that Windows is confusing the iPod with another storage device.  As a test, shut down (power off) your computer and disconnect all USB devices.  You can leave standard USB keyboard/mouse connected, if used.  If your computer is a laptop, connect its power supply so that it's not running on battery power.  Do a Reset (restart) on the iPod.

Learn how to reset your iPod - Apple Support  (See section iPod with a click wheel)

Start up your computer, run iTunes, and connect the iPod to a direct USB port on the computer, by itself.  Is there any difference?

I assume you already tried doing a Restore on the iPod using iTunes, but if you have not, do a Restore (in case the cause is data corruption on the iPod).  This erases the iPod, reinstalls its software, and sets it to default settings

Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings - Apple Support

If the problem still returns, the most likely cause is the hard drive becoming unreliable.

I have older iPods (4th gen and earlier), all upgraded to either Compact Flash or SD cards on the appropriate adapters.  They are BETTER now than when they were new, and now have much higher capacity.  The iFlash web site has a new adapter that allows two SD cards to be mixed and matched.  Very clever... 

Did you take a look at the web site?

https://www.iflash.xyz/

Two of the four ("Dual" and "Bundle") are for SD card (no additional adapter needed).

The shipping is only $10 for tracked airmail delivery, $3 (or maybe even free) for untracked airmail.  I've recently order some stuff from them, although my (working) iPods are too old to try their primary adapter products (which are for 5th gen and later iPods).  OWC sells some of their adapters, but the price is higher.

Email the guy who runs the operation.