Don't do any searching at the published coordinates, unless you are wearing a police uniform! (it's the parking lot for the police station 
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Located 13 miles from the Omaha VHF Omnidirectional Range (VOR), the GRETT intersection is used by aircraft flying in the clouds(as well as those flying in good weather) as reporting point. A named place that they will fly by on their way to Omaha, or a place where they will begin navigation away from Omaha.
GRETT can by identified by tuning two radios, The VOR reciever, and one of the following, A Non-Directional Beacon (NDB) at the Plattsmouth airport, or a Distance Measuring Equipment (DME) that communicates with the Omaha VOR. It can also be identified with a GPSr.
The cache is located as close as I could get and not have the cache plowed in the spring, or make the nearby police nervous 
. The coordinates are, of course, published, just not here. You have to know where to look for them. Once you get those coordinates, convert them to dd mm.mmm, then just add .051 to the longitude and you're there.
For Goodness Sake, Don't park on 72nd Street! Way too much comatose traffic on that street!
You can check your answers for this puzzle on Geochecker.com.