Luftwaffe Im Focus #3, page 37 shows the tail of Lt. Udo Cortes's Ju88 C-6, werk-nr. 360379. The caption states 5K+RT. Unfortunately the fuselage side codes are not visible in the photo. Don't know how the authors derived the fuselage code. Usually a clear photo of the fuselage code, eye-witness testimony, records, etc. would help, but I am not aware of any of these for Cortes's Ju 88 C-6, werk-nr. 360379.