GX50 datacard

I have an Apollo (now Garmin AT) GX50 GPS. The data card failed last
week. It will not take a program. I use Jeppesen's skybbound service
for updates.

Now, the card is a Linear 4 Mb Flash Disk.

Garmin wants $153 for a replacement card but these cards can be bought
anywhere for $60.

Does anyone know if there is anything special about the card? I'm
assuming that it is a stock card, but maybe Garmin writes a special file
to it. Maybe like a format system?

Has anyone tried inserting a generic flash card into the skywriter box
and attempting a program? Will it accept the card?

(My cynical nature leads me to believe that Garmin writes a file to the
card and that Jeppesen's skywriter looks for this file so that Garmin
can overcharge for replacement cards.)