Hi and welcome!
G5S504020033B36 should be ok
The firmwares have been available
here
But I have stored a
copy at box as well.
If you flash the firmware parts (zImage, rd.gz, hdapp.tgz) it must not affect the bootloader.
One known effect is, if the file you load and flash is too big, it wraps around the flash chip and overwrites the bootloader.
Note that rd.gr and hddapp.tgz must remain in their compressed form. During boot these files are uncompressed and loaded into ram.
Regards,
HWguru