I have a Herd seeder/ sander that I almost put grease in the gear box. The only reason I didn't was that the gear box faces up and I was a little worried that the upper bearing may not get as much lubrication with grease as it would with oil splashing about. I bought it used and the seeder fell over and all the oil leaked out of the vent. It didn't look like it was used without oil but I went through the gear box and replaced the seals and bearings. I also replaced both shafts since they were pitted. The cost was actually real cheap, maybe $60 for everything.