I recently tried to fix a tach on my JD 855. Watched the video and thought it would be an easy task. Ended up having to replace the tach. Seems like the needle had been secured using some type of sealant and I bent the shaft in trying to get it off. I did repair one on my Jubilee many years ago; reset the hours to 0000.0 after engine rebuilt. Still working fine.
In regard to differences in old vs. new tachs. Wonder why they couldn't have made them identical. Only thought I had was maybe original tachs were supplied by different suppliers and new tachs resemble that of one of the different suppliers. Anyone know for sure??