Is this an old non-HC SD card?
https://www.ebay.co.uk/itm/transcend...-/222713853091
I too am preparing for a RNS-E conversion. I don't need navigation, as long as I can get SD cards that work I am happy to go for an older unit.
The newer RNS-E units with chrome knob that can support newer memory cards, they are all a lighter grey colour than the D2 plastic?