Hi, welcome to the site.
The hard drive is definitely not interchangeable, because of the data on the drive. There is a PAL and NTSC version of the hard drive.
The optical drives, however, should not contain any format-specific data. I also do not believe the DVD burners have any specific "JVC data" on them (in the firmware). Generally speaking, all DVD recorders use off-the-shelf computer DVD burners, but are not encased in a metal box, nor do they have a plastic bezel on front. It's just a bare drive, guts on display. If you can match the drive in the recorder to a model, then you can swap out for a like model drive. Given that information, the JVC drives from a PAL equivalent MH30 should work.
I don't guarantee this assessment is correct, but it is highly likely.
It is worth the efforts/costs/risks for repairing this machine. It's an excellent DVD recorder. I will say that much!