I ordered the following LEDs from Lasfit, 921 912 W16W LED Reverse for $13.99 2 per package, and installed them today and no dreaded consist on when both are in the socket and housing jacket. I tried this once already and failed with regular LEDs.
These Lasfits have a built in resistor and they work. They are very brite! Really lights up the back when in reverse.
I will be checking and posting for the next week to see if I run into any electric/electronic gremlins.