There is a difference in the reverse idle gear from the 1928 to the later 29-31. The 28 gear did not have a lube hole drilled through the side of the gear. The 28 reverse idle gear received lubrication from a hole in the end of the shaft that had a small open ended cup inserted in the shaft end to catch the oil. Not a good design as metal particles from gear wear lodged into the shaft cup, sometimes causing premature wear to the reverse idler bushing and shaft. Sometimes the hole just became plugged. Use the plain reverse gear shaft, with the reverse gear that has the drilled hole.
If you want.....the new shafts have "O-rings" installed to seal the shaft in the casing also.