Logically it should be 108-4824 as the Stinsons in this registration series had consecutive c/ns. N6823M was 108-4823, N6825 was 108-4825 etc., etc.
The problem is that according to all records I can find c/n 108-4824 relates to Stinson 108 N4186G which is still current. I assume it must have been re-registered at some stage but can find no evidence so far.
Hope this may be of some assistance Peter.
Cheers
Rob