Lifter problems aren't common but do occur. They are easy to change and relatively cheap.
I'm not sure what relay you are talking about. The one that powers the KE controller is the overvoltage protection relay. Its a common problem, but, it doesn't usually occur twice on the same car as the new relays are improved. If you are burning the fuse I would check your alternator as the OVP relay protects by using a zener diode. It passes voltage over a threshold to ground through the fuse. If the alternator is not being regulated properly, high voltages could quickly blow the fuse.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician