So over the past few years, I would have an intermittent starting problem with the L3700 SU. After reading all the typical problems that have happened with the L3400 ( basically the same tractor ). In many cases the issue was the safety switch below the steering column. So over the past few years I have replaced it a couple times. Well.. It wouldn't turn over again last week and again this past weekend. I had an extra safety switch and plugged it in..Still no start. Plenty of power. Solenoid clicks..Just no start. Tapped the starter with a hammer....bang...fires up. Starter is now ordered from my local dealer..about 150.00.
I don't know that replacing the starter is all that justified. I have 3 B2150s and one BX2200. One of the B2150's has around 1750 hrs on it and it has exactly the disease you describe. I have had to reach in with a socket extension rod and tap the starter with a light hammer ping on the rod reaching the starter probably 5 times over the last couple of years. Maybe have to do that once out of 50 starts ? I had the BX2200 do it twice but far less often and much lower hours tractor. I have not felt a need to replace the starter yet.
Other posts on TBN have mentioned this. Some think it is wear in the starter. Some think it is a random thing where if the starter quits in exactly the right rotation position the last time you used it it sticks. Who knows.