Believe it or not Allison(now RR) have made the gearbox to fit multiple aircraft not just the Jetranger. There are some that use all the studs and some that don't, depending on the accessory or output fitted. Bell considered that they only needed to use three of the studs for their free wheel rear housing.(Not a heavy load bearing component)
The oil leak will probably not fix itself (wear in) there seems to be a bad batch of seals about at the moment, I went through 3 in my machine before there was no leak.
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