You installed the ELGO tape perfectly plumb, right? The tape slides through the guide nice and easy, right? Seems pretty intuitive and doesn't need any explanation, right?

That's probably part of the problem.

The tape guide needs to be installed so that it is slightly pulling the tape. Obviously, install per the manual, but if the tape is not being slightly pulled, the magnetic surface will eventually wear away. If it's slightly being pulled, it keeps the surface of the magnetic side off preventing it from wearing.

MCE has a "CAUTION" note: It is critical to ensure that the sensor is installed so that any mechanical contact between tape and sensor head is between the steel band and the polymer sensor guide. Adjust for a horizontal offset of 1 inch (25 mm) between the sensor metal face and the magnetic band so that contact between the steel side and the polymer guide is firmly forced. (This is on page 10 of their current install manual. Older units are similar.)

The newer guides have a plastic insert to help protect the tape on one side.