Just bought a used bush hog 3210. Ten feet of mower. Seller said he just replaced both gear boxes. Come to find out that the truth is he replaced left had gear box a year ago. replaced rh gear bos 3 months ago. Lh gear bos is leaking oil. Friend said to jsut fill full of grease because leaking gear boses on big mowers is common, especially bush hog brand. Truth or fiction? Do I need to pull the leaking gear box and rebuild it?