I have never replaced the K27 relay before. It is only used on the 124.034 and .036 cars. Looking in the ETM I can verify the location frame B 2/4 figure 12. this is from the print version. That figure shows it under the seat.
I have replaced numerous K9 or K10 aux fan relays or their fuses; checked the circuits many times at these relays and they are in the back of the fuse box.
Bosch Master, ASE Master, L1
33 years MB technician