Tom, I just changed mine a month or so ago...It's a piece of cake...
Make sure you purchase a SCSI drive..not an IDE..
Match the jump connector on the back end of the drive,,,to the same setting of your current drive...the rest is easy..
Remove the little screws at the front corners near the bender and opposite corner...also from the back edge of the board and the black screws on the bottom..
Flip it over to the top side again and carefully tilt the top cover..careful to rest the back against a wall[ribbon will still be connected..no need to disconnect this].
Remove the 4 screws holding the drive in place as well as the power wire and the SCSI ribbon...That's it!!! Put it back together with the new drive.
As for the drives..
They are getting hard to fine ..that is why I bought a couple for stock...let's see , my first one lasted 7plus years...this one will last another 7 years, and I have another...I am good for another 15 years..By then , maybe I'll replace the G1000!!!