Hi
I have a pilot with the family name Sack listed as missing in action on January 1st 1945, flying in II./JG 53.
http://www.ahs.no/ref_db/lw_loss_pub...?lossid=129659
The excellent 'Bodenplatte' book by John Manrho and Ron Pütz mention this briefly on page 245, where they can add the information that Fw. Sack returned to his unit at Huchenfeld after a few days.
I do not know if this is the one you are looking for. Two additional persons with the family name Sack is mentioned in my database, but not as pilots.
Regards,
Andreas B